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<p><a name="page_index"></a><a href="index.htm#warranty"><img src="ok.gif" alt="Marks content from authoritative sources or confirmed by my own personal experience" border="0" width="16" height="16"></a>    <strong>Exposure strategies
</strong>
for digital cameras with priority and fully manual exposure controls</p>

<p>On
this page&#151;</p>

<ul>
    <li>
      <p style="margin-bottom: 9"><a href="#who">Who's in Charge Here?</a></li>
    <li>
      <p style="margin-bottom: 9"><a href="#basics">Stops, Shutter Speed and Aperture</a></li>
    <li>
      <p style="margin-bottom: 9"><a href="#reciprocity">Reciprocity and Exposure Values</a></li>
    <li>
      <p style="margin-bottom: 9"><a href="#ec">Exposure Compensation Controls</a></li>
    <li>
      <p style="margin-bottom: 9"><a href="#strategies">Exposure Strategies</a></li>
    <li>
      <p style="margin-bottom: 9"><a href="#constraints">Guiding Constraints</a></li>
    <li><a href="#recording">Recording Mode�Critical Pre-Exposure Digital Decisions</a>
      <ul type="square">
        <li>
          <p style="margin-top: 9"><a href="#iso">ISO</a> and <a href="#noise">Noise</a></li>
        <li><a href="#color_mode">Color Mode</a></li>
        <li><a href="#resolution">Resolution</a></li>
        <li><a href="#compression">Compression and Color Interpolation</a></li>
        <li><a href="#sharpening">In-Camera Sharpening</a></li>
        <li><a href="#wb">White Balance</a></li>
      </ul>
    </li>
</ul>

<ul>
    <li>
      <p style="margin-bottom: 9"><a href="#resolving">Resolving Power</a></li>
    <li>
      <p style="margin-bottom: 9"><a href="#dof">Depth of Field (DOF)</a></li>
    <li>
      <p style="margin-bottom: 9"><a href="#hyperfocal">Hyperfocal
      Technique</a></li>
    <li>
      <p style="margin-bottom: 9"><a href="#motion">Motion Management</a></li>
    <li>
      <p style="margin-bottom: 9"><a href="#dynamic">Dynamic Range</a></li>
    <li>
      <p style="margin-bottom: 9"><a href="#tonality">Tonality</a></li>
    <li>
      <p style="margin-bottom: 9"><a href="#zone">The Zone System</a></li>
    <li>
      <p style="margin-bottom: 9"><a href="#thumb">Manual Exposure Rules of Thumb</a></li>
    <li>
      <p style="margin-bottom: 9"><a href="#advanced">Advanced
      Digital Exposure Considerations</a></li>
    <li>
      <p style="margin-bottom: 9"><a href="#editor">Editor's Note</a></li>
    <li>
      <p style="margin-bottom: 9"><a href="#rules">Editorial: The Proper Role
      For Rules</a></li>
    <li><a href="#references">References and Links</a></li>
</ul>

<h5>See also the <a href="c-2000z/checklists/index.htm#hyperfocal">Hyperfocal
Checklist</a></h5>

<p>Last updated <!--webbot bot="Timestamp" S-Type="EDITED"
S-Format="%B %d, %Y" startspan -->October 22, 2009<!--webbot bot="Timestamp" i-checksum="31107" endspan --></p>

<hr>

<h2><a name="who"></a><strong>Who's in Charge Here?</strong></h2>

<p>This article's all about seizing control of exposure. If you don't, the
camera will, and the result won't always be what you had in mind. It may or may not be worth taking
control of exposure at the company picnic, but when the stakes or aims are high, you can
improve your odds substantially by stepping in.</p>

<hr>

<h3><a name="vision"></a>Inner Vision</h3>

<p>Your camera's built-in
metering system will seldom have trouble coming up with technically &quot;correct&quot;
exposures. In some situations, that's all you'll need, but
don't expect the meter to offer exposure settings optimized for your <i> photographic
goals</i> in a particular scene. Those goals are almost always driven by things the camera knows
absolutely nothing
about�things I'll lump together under the term <i>inner vision</i>:</p>

<ul>
  <li>
    <p style="margin-bottom: 9">what <i>you</i> see in the scene, in the broadest sense of <i>seeing</i></li>
  <li>
    <p style="margin-bottom: 9">what <i>you</i> deem to be the scene's <i>most important
    elements</i></li>
  <li>
    <p style="margin-bottom: 9">the <i>emotional response</i> the scene evokes in <i>you</i></li>
  <li>
    <p style="margin-bottom: 9">what you'd like <i>other humans</i> to see and
    feel in your
    photograph</li>
</ul>
<p>Capturing that inner vision is the ultimate goal of any serious photograph,
but the gulf separating what the human <a href="vision.htm#brain-eye">brain-eye system</a> sees and feels in the
scene and what even the most sophisticated camera senses in the frame is wide
and deep. By taking control of exposure and composition, you actively manage that
gap to align your vision and the camera's capabilities as best you can.&nbsp;Reducing
the gap may make a huge difference, even if you can't fully close it.</p>

<p>Here we'll tackle exposure and related issues with a digital slant. For the composition piece,
which is no different on the digital than on the film side, I
heartily recommend Brian Peterson's book <i><a href="http://www.watsonguptill.com/0817441778.htm">Learning to See Creatively�How
to Compose Great Photographs</a></i> and practice, practice, practice.</p>

<hr>

<h3>Issues to Face</h3>

<p>Your camera knows nothing of the <a href="#motion">motion</a> and <a href="#dof">depth
of field</a> challenges you face. Left to its own devices, it will render
whatever it's metered in a <a href="#medium"> medium tone</a>, regardless of the <a href="#tonality">tonality</a>
you actually see or want. And it may well put what it knows of the performance of its own
lens ahead of considerations far more import to you. To cut the best deal
across all these critical fronts�<a href="#tonality">tonality</a>, <a href="#dof">depth
of field</a>, <a href="#motion">motion management</a> and <a href="#resolving">resolving
power</a>�you're going to have to step in.&nbsp;</p>

<p> If your camera's
built-in TTL metering system offers exposure locking and
reasonably tight spot metering, as do most current higher-end digital cameras,
its exposure <i>suggestions</i> can serve as a solid <i>starting point</i> for all your
exposure judgements. Your <a href="#vision">inner vision</a> and the <a href="#rules">rules</a>
of photography will guide you from there.&nbsp;</p>

<blockquote>

<p><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;<b><i>Only you can see the picture you've envisioned for the scene before
you, and only you can make the technical trade-offs needed to capture it with
the equipment at hand.</i></b></p>

</blockquote>

<table border="0">
    <tr>
        <td valign="top"><em><strong><a href="#strategies"><img src="bypass.gif"
        alt="Marks opportunities to bypass long-winded discussions and cut to the action line. Click to review Limited Warranty section on the home page."
        align="texttop" border="0" width="36" height="30"></a></strong></em></td>
        <td valign="top">If you're already familiar with concepts like stops,
          shutter speed and aperture, click at left to skip ahead to <a href="#strategies">exposure
          strategies</a> now. To review exposure basics, read on.</td>
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<hr>

<h2><a name="basics"></a><strong>Stops, Shutter Speed and Aperture</strong></h2>

<p>For anyone who needs it, the next few sections offer a leg up on the definitions and
science behind basic photographic terms like <a href="#stops">stop</a>, <a href="#duration">shutter
speed</a>, <a href="#aperture">aperture</a>, <a href="#f-number">f-number</a>, <a href="#reciprocity">reciprocity</a>,
<a href="#ev">exposure value (EV)</a> and <a href="#ec">exposure compensation
(EC)</a>.
Without a solid understanding of these basic building blocks, the rest of the article
won't make much sense.&nbsp;</p>

<hr>

<h3><b><a name="stops"></a>Stops</b></h3>

<p>In photographic parlance, a <i>stop</i> or <i>full stop</i> is simply a
factor of 2 change in the amount
of light fed to the image receiver in the course of image capture. Increasing exposure by a stop doubles
the light input, and decreasing exposure by a stop
halves it.</p>

<blockquote>

<p><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;<b>Think of a
stop as a unit of exposure or light input divorced from the details of how it's
achieved.</b>&nbsp;</p>

</blockquote>

<p>On film cameras, stops are still real click-stops on mechanical shutter speed dials
and lens aperture rings,
but electronic controls have largely robbed the term &quot;stop&quot; of its
mechanical meaning on the digital side.&nbsp;</p>

<p>But even disembodied stops remain useful because they correspond perceptually
to more or less evenly spaced gradations of light and dark. Stops give us an easy way to talk
and think about the <a href="vision.htm#brain-eye"> brain-eye system</a>'s final linear response to exponential variations in
light input. (The auditory and visual systems both deal in logarithms of input
amplitudes.) Film and digital camera designers work hard to emulate this
log-linear response so that photographers can rely on their natural sense of
tonality.</p>

<p>Since stops correspond to powers of two in light input, they're relatively
easy to figure in your head. They also nicely scale the effective <a href="#dynamic">dynamic
ranges</a> afforded by most film and digital cameras in a manageable number of
log-linear steps�usually 3-8 stops.</p>

<p><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;When photographers speak of &quot;opening up a stop&quot; or &quot;stopping
down&quot;, they're usually talking about adjusting exposure by the most
appropriate means, not just via <a href="#aperture">aperture</a> changes. That's
the way I'll use such terms below.</p>

<hr>

<h3><b><a name="duration"></a>Shutter Speed</b></h3>

<p><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;For a given
scene and lens, the amount
of light fed to the image receiver is completely
determined by the product of exposure time and aperture area.</p>

<p>Because of the way the exposure duration is actually controlled inside film cameras,
the term <i>shutter speed</i> is often substituted for exposure time,
but to call for an exposure of 1/250 sec is clearly to specify a duration, not a
speed. Strictly speaking, the concept of shutter speed doesn't even apply to the subset of digital cameras
with electronic rather than mechanical &quot;shutters&quot;, but the terminology is firmly
entrenched and will likely remain so.</p>

<p>
Since exposure varies linearly with exposure time, a stop in speed is simply a
doubling or halving of exposure. The shutter speed dials on most 35 mm SLRs
come with click-stops at 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250,
1/500, and perhaps even 1/1000 sec and beyond. Many digital cameras emulate this
familiar sequence of full stops, and some higher-end digitals like the Oly
Camedias insert partial stops as well.</p>

<hr>

<h3><b><a name="aperture"></a>   Aperture and f-stops</b></h3>

<p>Opening the lens aperture a full <a href="#stops">stop</a>  by definition doubles the amount of light allowed to reach the
image receiver, be it film or CCD. Stops of aperture are often called <i>f-stops.</i></p>

<p> Doubling the light input via aperture requires a
doubling of the
aperture area. For the roughly circular iris apertures
still in common use�even in digital cameras�that means opening the iris diameter by a factor of sqrt(2) or ~1.4.</p>

<h4><a name="f-number"></a>F-numbers</h4>

<p>Aperture diameters have come to be expressed as fractions of lens
focal length (f), a notation that tremendously simplifies exposure
considerations by divorcing aperture designations from the particulars of lens
focal length.&nbsp;</p>

<p> For a digital lens with an actual focal length of 14 mm, f/2.8
denotes a 5 mm aperture, where the 2.8 is known as the <i>f-number</i>. On a 35
mm SLR with its zoom lens set at 140 mm, f/2.8 means a 50 mm iris opening
(that's one reason fast telephoto lenses are so large). The physical iris openings
differ greatly in these two examples, but at f/2.8, both lenses make the same
contribution to exposure. F-numbers
corresponding to full stops are roughly whole-number powers of the square root of
2.&nbsp;</p>

<p>In the table below, the f-numbers corresponding to full f-stops appear in bold; the
intervening apertures represent the so-called &quot;1/3&quot; and
&quot;2/3&quot; stops. For now, the seemingly arbitrary &quot;stop numbers&quot;
shown are useful for figuring the number of stops (exposure doublings) between
any two aperture settings, but they'll later reappear as <a href="#ev2">exposure values</a>. Note their
negative logarithmic relationship to the relative aperture area.</p>

<div align="left">
  <table border="2">
    <tr>
      <td colspan="3">
        <h4><b>f-stops</b></h4>
      </td>
    </tr>
    <tr>
      <td>f-number</td>
      <td>stop number</td>
      <td>relative aperture area&nbsp;</td>
    </tr>
    <tr>
      <td valign="top" align="right"><b>1.0</b></td>
      <td valign="top" align="right"><b>0</b></td>
      <td valign="top" align="right"><b>512</b></td>
    </tr>
    <tr>
      <td valign="top" align="right"><b>1.4</b></td>
      <td valign="top" align="right"><b>1</b></td>
      <td valign="top" align="right"><b>256</b></td>
    </tr>
    <tr>
      <td valign="top" align="right"><b>2.0</b></td>
      <td valign="top" align="right"><b>2</b></td>
      <td valign="top" align="right"><b>128</b></td>
    </tr>
    <tr>
      <td valign="top" align="right">2.2</td>
      <td valign="top" align="right">&nbsp;</td>
      <td valign="top" align="right">104</td>
    </tr>
    <tr>
      <td valign="top" align="right">2.5</td>
      <td valign="top" align="right">&nbsp;</td>
      <td valign="top" align="right">80</td>
    </tr>
    <tr>
      <td valign="top" align="right"><b>2.8</b></td>
      <td valign="top" align="right"><b>3</b></td>
      <td valign="top" align="right"><b>64</b></td>
    </tr>
    <tr>
      <td valign="top" align="right">3.2</td>
      <td valign="top" align="right">&nbsp;</td>
      <td valign="top" align="right">52</td>
    </tr>
    <tr>
      <td valign="top" align="right">3.6</td>
      <td valign="top" align="right">&nbsp;</td>
      <td valign="top" align="right">40</td>
    </tr>
    <tr>
      <td valign="top" align="right"><b>4.0</b></td>
      <td valign="top" align="right"><b>4</b></td>
      <td valign="top" align="right"><b>32</b></td>
    </tr>
    <tr>
      <td valign="top" align="right">4.5</td>
      <td valign="top" align="right">&nbsp;</td>
      <td valign="top" align="right">24</td>
    </tr>
    <tr>
      <td valign="top" align="right">5.0</td>
      <td valign="top" align="right">&nbsp;</td>
      <td valign="top" align="right">20</td>
    </tr>
    <tr>
      <td valign="top" align="right"><b>5.6</b></td>
      <td valign="top" align="right"><b>5</b></td>
      <td valign="top" align="right"><b>16</b></td>
    </tr>
    <tr>
      <td valign="top" align="right">6.3</td>
      <td valign="top" align="right">&nbsp;</td>
      <td valign="top" align="right">13</td>
    </tr>
    <tr>
      <td valign="top" align="right">7.0</td>
      <td valign="top" align="right">&nbsp;</td>
      <td valign="top" align="right">10</td>
    </tr>
    <tr>
      <td valign="top" align="right"><b>8.0</b></td>
      <td valign="top" align="right"><b>6</b></td>
      <td valign="top" align="right"><b>8</b></td>
    </tr>
    <tr>
      <td valign="top" align="right">9.0</td>
      <td valign="top" align="right">&nbsp;</td>
      <td valign="top" align="right">6</td>
    </tr>
    <tr>
      <td valign="top" align="right">10.0</td>
      <td valign="top" align="right">&nbsp;</td>
      <td valign="top" align="right">5</td>
    </tr>
    <tr>
      <td valign="top" align="right"><b>11.0</b></td>
      <td valign="top" align="right"><b>7</b></td>
      <td valign="top" align="right"><b>4</b></td>
    </tr>
    <tr>
      <td valign="top" align="right"><b>16.0</b></td>
      <td valign="top" align="right"><b>8</b></td>
      <td valign="top" align="right"><b>2</b></td>
    </tr>
    <tr>
      <td valign="top" align="right"><b>22.0</b></td>
      <td valign="top" align="right"><b>9</b></td>
      <td valign="top" align="right"><b>1</b></td>
    </tr>
  </table>
</div>
<p>Technical Note: The conventional shutter speeds and f-numbers
found in the table and text above deviate slightly from the numbers that would follow
from a strict adherence to the physics underlying the table. Whether these minor
discrepancies reflect practical conveniences, rounding errors, conventions or something else,
I don't know, but no one seems to care. They're now firmly entrenched in
photographic practice.</p>

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<hr>

<h2><b><a name="reciprocity"></a>Reciprocity
and Exposure Values</b></h2>

<p>One would like to think that the same amount of light delivered to the image
receiver would result in the same exposure, regardless of the rate of delivery.
In other words, blasting the receiver with a certain total dose of light in a
short time should have the same effect as dribbling in the same dose over a
longer duration. This concept is known as <i>reciprocity</i>, and fortunately, it holds up under
most circumstances.&nbsp;</p>

<p>Reciprocity means that you can safely rely on a perfectly <b>reciprocal relationship between
aperture and exposure time</b>: If you open up one full stop in aperture
to double the aperture area while halving the exposure time, the resulting film
density or CCD charge remains the same. The <a href="#ev_table">exposure value table</a>
below nicely demonstrates
the reciprocity relationship.</p>

<hr>
<h3>Using Reciprocity</h3>

<p><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;Once you decide to take control of exposure, reciprocity becomes one of your
most important tools. It allows you to work your way from a technically correct
but often artistically challenged exposure determined by a light meter to an equivalent exposure carefully matched
to your photographic intent.</p>

<p>By reciprocity, f/2 @ 1/500 sec, f/5.6 @ 1/60 sec and
f/11 @ 1/15 sec are all equivalent exposures at <a href="#ev">EV</a> = 11, but only the first would be suitable for
<a href="#stop-action">stop-action</a> shots at a basketball game. The first two
settings could be handheld, but the third would probably fall prey to <a href="#shake">camera
shake</a> in anyone's hands.</p>

<hr>

<h3><b><a name="failure"></a>Reciprocity Failure</b></h3>

<p>Unfortunately, for film at least, reciprocity tends to break down at very
long (multisecond) and very short exposure times such that greater than expected
increases in exposure time become
necessary to compensate for a given decrease in aperture�hence the term <i>reciprocity failure</i>.</p>

<p>To what extent reciprocity failure might apply to digital cameras, I'm not
sure. CCDs are said to be very linear devices, and their exposure-charge curves
probably don't have much of a toe. Clipping of the
shoulder of the exposure-charge curve at high exposures due to <a href="#bloomng">blooming</a>
amounts to a reciprocity failure of sorts.&nbsp;So does the draining off of
excess photoelectrons to mitigate blooming in many CCDs.</p>

<hr>

<h3><b><a name="ev"></a>Exposure Values (EVs)</b></h3>

<p>Exposure values provide a convenient way to quantify available light
intensity and therefore exposure. In the Additive Photographic Exposure System
<a href="#ev_table">EV table</a> below, <i>exposure value</i>
(EV) is defined as the sum of the respective stop numbers corresponding to the
aperture and exposure time of interest, with one unit of EV corresponding to one
stop of exposure.</p>

<blockquote>

<p><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;<b>Think of EV
as a measure of available light intensity as the camera's meter sees it,
divorced from the details of how the camera might go about acquiring it.</b></p>

</blockquote>

<p>A bright scene metered at EV 12 reflects more light to the camera than a
darker scene metered at EV 8 by a factor of 16, or 4 stops. Conversely, a camera
metering a scene at EV 8&nbsp; is 4 stops more sensitive (requires 16 times less
light input for proper exposure) than a different (or differently adjusted)
camera metering the same scene at EV 4. The difference in sensitivity in the
latter example might well reflect a difference in <a href="#iso">ISO settings</a>.</p>

<p>As available light instensity and therefore metered EV increase, the exposure
called for by the meter (i.e., the amount of light to be admitted by the camera)
must <i>decrease</i> in order to maintain proper stimulation of the image
receiver. In other words, as available light intensity increases, the camera
must either stop down the <a href="#aperture">aperture</a> or decrease <a href="#duration">exposure
time</a> or both to avoid overexposure.&nbsp;</p>

<p>Note that this standard definition of EV runs counter to the way <a href="#ec">exposure compensation</a>
 (EC) controls are typically marked. When you increase EC by +1.0, you're
forcing the camera to admit twice as much light as the meter suggested. But
that's what the meter would have called for if the scene had somehow darkened by
EV -1.0. EV and EC are measured in the same units (stops) but run in opposite
directions.</p>

<p>Luckily, none of that makes much difference in common practice. What really counts
most of the time is what happens at <i> constant</i> EV�the one
corresponding to the correct exposure determined by your meter:</p>

<blockquote>

<p><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;<b>In the
absence of <a href="#failure">reciprocity failure</a>, all aperture and shutter speed
combinations yielding the same EV produce equivalent exposures.</b>&nbsp;</p>

</blockquote>

<p>This very powerful result allows you to optimize your technique for <a href="#dof">DOF</a>,
<a href="#resolving">resolving power</a>, <a href="#shake">motion control</a>, <a href="#tonality">tonality</a>
or
whatever's most important at the scene, without compromising exposure.&nbsp;That's
what <a href="#reciprocity">reciprocity</a> is all about.&nbsp;&nbsp;</p>

<h4>Using the Additive EV Chart</h4>

<p>To get the EV for any given exposure from the chart below, simply <i>add</i>
the stop numbers corresponding to the desired aperture and exposure time. Thus,
the EV for f/2.0 @ 1/8 sec = 2 (from the aperture column) + 3 (from the time
column) = 5.&nbsp;</p>

<div align="left">
  <table border="2" width="352" height="508">
    <tr>
      <td colspan="3" width="340" height="32" valign="top">
        <h4><b><a name="ev_table"></a>additive exposure value (ev) table</b></h4>
      </td>
    </tr>
    <tr>
      <td width="97" height="56" valign="top">stop number*</td>
      <td width="111" height="56" valign="top">exposure time (sec)</td>
      <td width="120" height="56" valign="top">aperture (f-number)</td>
    </tr>
    <tr>
      <td valign="top" align="left" width="97" height="28">0</td>
      <td align="center" valign="top" width="111" height="28">1</td>
      <td align="right" valign="top" width="120" height="28">1.0</td>
    </tr>
    <tr>
      <td valign="top" align="left" width="97" height="28">1</td>
      <td align="center" valign="top" width="111" height="28">1/2</td>
      <td align="right" valign="top" width="120" height="28">1.4</td>
    </tr>
    <tr>
      <td valign="top" align="left" width="97" height="28">2</td>
      <td align="center" valign="top" width="111" height="28">1/4</td>
      <td align="right" valign="top" width="120" height="28">2.0</td>
    </tr>
    <tr>
      <td valign="top" align="left" width="97" height="28">3</td>
      <td align="center" valign="top" width="111" height="28">1/8</td>
      <td align="right" valign="top" width="120" height="28">2.8</td>
    </tr>
    <tr>
      <td valign="top" align="left" width="97" height="28">4</td>
      <td align="center" valign="top" width="111" height="28">1/15</td>
      <td align="right" valign="top" width="120" height="28">4.0</td>
    </tr>
    <tr>
      <td valign="top" align="left" width="97" height="28">5</td>
      <td align="center" valign="top" width="111" height="28">1/30</td>
      <td align="right" valign="top" width="120" height="28">5.6</td>
    </tr>
    <tr>
      <td valign="top" align="left" width="97" height="28">6</td>
      <td align="center" valign="top" width="111" height="28">1/60</td>
      <td align="right" valign="top" width="120" height="28">8.0</td>
    </tr>
    <tr>
      <td valign="top" align="left" width="97" height="28">7</td>
      <td align="center" valign="top" width="111" height="28">1/125</td>
      <td align="right" valign="top" width="120" height="28">11.0</td>
    </tr>
    <tr>
      <td valign="top" align="left" width="97" height="28">8</td>
      <td align="center" valign="top" width="111" height="28">1/250</td>
      <td align="right" valign="top" width="120" height="28">16.0</td>
    </tr>
    <tr>
      <td valign="top" align="left" width="97" height="28">9</td>
      <td align="center" valign="top" width="111" height="28">1/500</td>
      <td align="right" valign="top" width="120" height="28">22.0</td>
    </tr>
    <tr>
      <td valign="top" align="left" width="97" height="28">10</td>
      <td align="center" valign="top" width="111" height="28">1/1000</td>
      <td align="right" valign="top" width="120" height="28">32.0</td>
    </tr>
    <tr>
      <td valign="top" align="left" width="97" height="28">11</td>
      <td align="center" valign="top" width="111" height="28">1/2000</td>
      <td align="right" valign="top" width="120" height="28">45.0</td>
    </tr>
  </table>
</div>

<h5><b>* Technical note:</b> The stop numbers in the table above are
actually base-2 logarithms of the reciprocal of <a href="#duration"> exposure time</a>
and the square of the <a href="#f-number"> f-number</a>, respectively. The
addition of stop numbers reflects the fact that&nbsp;&nbsp;</h5>

<div align="left">
  <blockquote>
    <table border="0">
      <tr>
        <td>
          <h5>EV</h5>
        </td>
        <td>
          <h5>= log<sub>2 </sub>(a<sup>2</sup>/t)</h5>
        </td>
      </tr>
      <tr>
        <td>
          <h5></h5>
        </td>
        <td>
          <h5>= log<sub>2 </sub>a<sup>2</sup> + log<sub>2 </sub>(1/t)&nbsp;</h5>
        </td>
      </tr>
      <tr>
        <td>
          <h5></h5>
        </td>
        <td>
          <h5>= 2 * log<sub>2 </sub>a - log<sub>2 </sub>t</h5>
        </td>
      </tr>
    </table>
  </blockquote>
</div>

<h5>where <i>a</i> is the aperture <a href="#f-number"> f-number</a> (again, the 2.8 in f/2.8), <i>t</i>
is the <a href="#duration"> exposure time</a> in seconds, and <i>log<sub>2</sub></i> is the logarithm to the
base 2. The coefficients and signs in the last version of the equation
are simply built into the table for convenience. (For those rusty on their base-2 logarithms, log<sub>2</sub>  (1/x) = -log<sub>2</sub> 
x, log<sub>2</sub> 1 = 0, log<sub>2</sub>
2 = 1, log<sub>2</sub> 4 = 2, log<sub>2</sub> 128 = 7, log<sub>2</sub> 1024 =
10, and so on.) The conventional exposure times and f-numbers listed approximate
whole-number powers of sqrt(2).</h5>

<h4>EV Example</h4>

<p> Suppose you select f/2.8 in aperture-priority
mode and your camera meters a shutter speed of 1/250 sec. From the table, EV = 3
+ 8 = 11 for f/2.8 @ 1/250 sec. Now you can move to any other EV = 11 combination that
fits your needs�for example, f/2 @ 1/500 sec for better <a href="#motion">motion
resistance</a>, f/4 @ 1/125 for better <a href="#resolving_sweet">resolving
power</a> or f/5.6 @ 1/60 sec for greater <a href="#dof">depth of field</a>�and still get the same exposure.</p>

<hr>

<h3><a name="priority"></a><b>Priority Metering</b></h3>

<p>Note that this constant-EV calculation is precisely what <i>priority metering</i> does for you
automatically: The
camera meters the scene to determine the proper EV. The firmware then works to
maintain that EV as you take control of either aperture or shutter speed to
optimize your technique.</p>

<p>The <b> biggest risk</b> with priority metering lies in the fact that you can easily
<i>and unknowingly</i> take exposure beyond the camera's ability to follow�for example, by setting a fast shutter speed in shutter-priority mode in
low light requiring an f/1.4 aperture when f/2 is the widest aperture the
camera can deliver. When my C-2020Z's main LCD is on, the parameter I'm controlling turns
red when the camera can't hack a suitable setting for the parameter it's
controlling. When the
LCD's off, I can proceed unaware that the camera's fallen off the wagon.</p>

<blockquote>

<p><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;<b>Only
vigilant <a href="#monitoring">exposure
monitoring</a> can keep you from straying outside your camera's exposure
envelope in the priority modes.</b>&nbsp;</p>

</blockquote>

<p>To guide manual exposures using the firmware's constant-EV calculator,
I sometimes duck into a priority mode temporarily to get the camera to work out
equivalent exposures for me. Once I see a combination close to what I'm after, I
return to manual mode, dial it in, make the necessary adjustments and shoot.</p>

<p>I find it well worth the battery hit to keep my LCD and exposure display on
whenever I'm using priority or manual exposure.</p>

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<hr>

<h2><b><a name="ec"></a>Exposure Compensation Controls</b></h2>

<p><i>Exposure compensation</i>  or <i>exposure correction</i> (EC) controls provide an easy way to bias an exposure
by 2-3 full <a href="#stops"> stops</a> up or down from the camera's metered aperture and shutter speed, usually in 1/2- to 1/3-stop increments. EC is particularly
useful for manual <a href="#bracketing">bracketing</a> and for overriding the
camera's exposure theory in priority
modes, where EC adjusts only the exposure setting left to the camera's
control. In auto or program mode, EC again allows intentional under- or overexpose
relative to the firmware's exposure strategy, but I have yet to figure out how the
bias gets apportioned between aperture and shutter speed in auto mode. My Oly C-2020Z doesn't
support EC in manual mode, probably because it doesn't make much sense in that
context.</p>
<p>What good is EC? For starters, many digital cameras behave like color slide
film�the best images are often slightly underexposed, particularly when bright
scene elements are present. EC is the fastest and simplest way to underexpose.
In bright sunlight, my C-2020Z tends to do its best work at EC -0.3 or -0.7.
With EC and a little effort, you can easily feel out your own camera's exposure
sweet spots, but count on variation with photographic conditions, as <b>dp<i>FWIW</i></b>
contributor <a href="index.htm#lackamp">Tom Lackamp</a> details in his <a href="#advanced">take
on digital exposure</a> below.</p>
<p> In landscape and close-up work, <a href="#dof"> depth of field</a>
requirements typically dictate a specific aperture, but what if <a href="#tonality">tonality</a>
requires an <a href="#ev">EV</a> different from
the one your camera deems appropriate? If the desired EV is less than 2-3 stops
from the meter's EV, EC makes it
simple to go there in
aperture-priority mode without altering the aperture <i>and</i> without
resorting to full manual exposure.</p>
<hr>
<h3>Using EC</h3>
<p>If you're unfamiliar with EC, the fastest way to learn is to play around with your EC control
and
watch its effect on exposure settings. (Most cameras display exposure settings
on their rear LCDs if nowhere else, but you may need to half-press the shutter release
to update them.)</p>

<p>Technically speaking, the EC controls in most cameras are calibrated in
<i>negative</i>   <a href="#ev">EV</a> units, presumably to avoid confusing the preponderance of
owners tempted to use them but unaware of the formal definition of EV. On every EC-enabled camera I've ever seen, digital or otherwise, for each positive unit of added EV, exposure
doubles, and for each negative unit,
exposure halves. That works for me, but as you run down the <a href="#ev_table">standard
EV
table</a> above, just the opposite obtains�for every positive unit of added
EV, exposure drops by a half.</p>

<p>Perhaps an example will make this less confusing. Say your camera's in aperture-priority mode at f/4 and the
meter sees an EV of 12, which calls for a shutter speed of 1/250 sec for a
proper exposure. Since you've fixed the aperture, if
you set EC = +1, you'll get f/4 @ 1/125 (double the time, EV = 4 + 7 = 11), and if you
set EC = -1, you'll get f/4 @ 1/500 (half the time, EV = 6 + 7 = 13).&nbsp;</p>

<p>Still confused about EC vs. EV? Well, at least now you'll feel justifiably
so.</p>

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<hr>

<h2><b><a name="strategies"></a>Exposure
Strategies</b></h2>

<p>Now that we've examined the physical basis of exposure and the means for
controlling it, let's talk strategy.</p>

<p>First of all, there's nothing wrong with using the automatic or program
exposure mode in your digital camera�<i>provided</i> it gives you the image
you're after. Automatic metering systems in today's cameras are very adept at
coming up with reasonable exposures based on available light, various camera
settings and known properties of the camera's lens or sensor. But blind
acceptance of automatic exposures amounts to playing dice on the artistic, <a href="#vision">inner
vision</a> side of the equation, with the house odds stacked against
ending up with an optimum exposure. Of course, an <a href="#ev">EV</a>
different from the meter's is out of the question without intervention.</p>

<p><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>    The trick, of
course, is to learn when and how to depart from the camera's inclinations, and that's where
<a href="#tonality">tonality</a>,&nbsp;<a href="#motion"> motion control</a>, <a href="#reciprocity">reciprocity</a>,
<a href="#ec">exposure compensation</a>, and manual exposure
come in.
The very effective semi-automatic aperture- and shutter-priority exposure modes
available in many digital cameras play the reciprocity game for you: You seize
control of aperture or shutter speed, and the camera varies the other
automatically to maintain the metered EV within the camera's exposure envelope.
Often, this is all the control you need to get the shot in your mind's eye, but higher-end digital cameras with <a href="#ec">exposure compensation</a> and
fully manual exposure allow you break the bonds of camera-imposed exposures to
reach the <a href="#tonality">tonality</a>  and<a href="#motion"> motion control</a>
you had in mind.</p>
<hr>
<h3><b>A Stepwise Approach to Exposure</b></h3>

<p>Some master photographers can divine exposures with amazing accuracy without
the aid of a meter. Others prefer to rely on calibrated external meters and manual exposure
control. For the rest of us, it's perfectly reasonable to use the camera's
automatic metering as a <i>starting point</i>�provided one can handle the inevitable
    exposure trade-offs ahead.</p>

<p>Here's the overview from 35,000 feet:</p>
<ul>
  <li>
    <p style="margin-bottom: 9">Decide how you want to handle basic pre-exposure
    issues like <a href="#resolution">resolution</a>, <a href="#compression"> compression level</a> and
    <a href="#sharpening"> in-camera sharpening</a>,
    preferably through testing.</li>
  <li>
    <p style="margin-bottom: 9">Starting with the camera's metering, use <a href="#reciprocity">reciprocity</a> and
    <a href="filters.htm"> filters</a> as needed to
    achieve just the right combination of <a href="#iso">ISO</a>, <a href="#aperture">aperture</a>, <a href="#duration">shutter
    speed</a> to make the picture in your mind's eye
    using the <a href="#constraints">guiding constraints</a> detailed below. A
    priority mode will often suffice.</li>
  <li>
    <p style="margin-bottom: 9">As needed, escalate to <a href="#ec">exposure compensation</a>  (in a priority
    mode) or even manual mode to override
    the camera's meter to achieve proper <a href="#tonality">tonality</a>.</li>
</ul>
<p>And here's the blow-by-blow approach:</p>
<ol>
  <li>
    <p style="margin-bottom: 9">First, set <a href="#iso">ISO</a>, choosing the
    lowest setting feasible for the task at hand. <a href="#stop-action">Action shots</a>
    are one of the best reasons to venture beyond minimum ISO. It's generally best to avoid camera
settings that allow the camera to change <a href="#iso">ISO</a>.</li>
  <li>
    <p style="margin-bottom: 9">If you already know that aperture will be your critical setting�say, in
landscape or close-up work�dial in your aperture in aperture-priority mode and
work from there.
If shutter speed is key�as it would be in <a href="#stop-action"> action shots</a>, for instance�start
by setting shutter speed in shutter-priority mode.</li>
  <li>
    <p style="margin-bottom: 9">Next, <a href="#monitoring">check your exposure display</a>
to confirm that the setting left to the camera's control is consistent with your
photographic goals <i> and</i> the camera's abilities. If not, try using the <a href="#ec">exposure compensation</a>
 (EC) control to bend the camera to your needs. If EC's leeway (typically 2-3 stops
    on either side of
the camera's opinion) isn't enough to reach your target exposure in a priority
mode, resort to manual mode if available.</li>
  <li>As long as time's on your side, testing and <a href="#bracketing"> bracketing</a> are dirt cheap with
digital cameras. Don't be afraid to go out on a limb�it's the best way to
learn, and it's never been safer.</li>
</ol>

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<hr>

<h2><a name="constraints"></a><strong>Guiding Constraints</strong></h2>

<p>As we've already seen, there are many ways to skin the exposure cat. Rather than work off a recipe, learn to make exposure trade-offs to suit your own tastes and further your own
photographic goals. To get there,
you'll need to&nbsp;</p>
<ul>
  <li>
    <p style="margin-bottom: 9">Know exactly what's at stake with your exposure choices.</li>
  <li>Experiment like crazy to develop a feel for exposure and the trade-offs
    involved.</li>
</ul>
<p>Luckily, the feel will come surprisingly quickly with the <a href="digital.htm#feedback"> instant feedback</a>
and <a href="digital.htm#freedom">freedom to screw up</a>  digital photography
alone affords.</p>
<hr>
<h3><b>Narrowing the Choices</b></h3>
<p>Exposure decisions can be exceedingly complex, with many variables to juggle.
To navigate this jungle of seemingly endless choices, you need a path leading
from the scene and equipment at hand to the photo you want to capture�the one
that conveys the order and emotion unique to your vision.&nbsp;</p>
<p><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>      With the
photographic goal firmly in mind to help you prioritize your choices, the <b> exposure constraints</b> 
below will guide your path.</p>
<table border="2" width="789">
  <tr>
    <td valign="top" align="left" width="175">
      <h4><b>Constraint</b></h4>
    </td>
    <td valign="top" align="left" width="320">
      <h4><b>Primary Camera Controls</b></h4>
    </td>
    <td valign="top" align="left" width="270">
      <h4><b>Main Trade-offs&nbsp;</b></h4>
    </td>
  </tr>
  <tr>
    <td valign="top" align="left" width="175"><a href="#noise">Recording mode</a></td>
    <td valign="top" align="left" width="320"><a href="#iso">ISO</a>, <a href="#resolution">resolution</a>,
      <a href="#recording">compression</a>,
      <a href="#sharpening">in-camera sharpening</a></td>
    <td valign="top" align="left" width="270">Useable <a href="#aperture"> apertures</a>
      and <a href="#duration">shutter speeds</a>, file size, image quality, post-processing
      and printing options, <a href="#memory">memory capacity</a> and <a href="#latency">shot-to-shot
      latency</a></td>
  </tr>
  <tr>
    <td valign="top" align="left" width="175"><a href="#resolving">Resolving power</a>&nbsp;</td>
    <td valign="top" align="left" width="320">Aperture, magnification</td>
    <td valign="top" align="left" width="270">Shutter speed or <a href="#iso">ISO</a></td>
  </tr>
  <tr>
    <td valign="top" align="left" width="175"><a href="#dof">Depth of field</a>&nbsp;</td>
    <td valign="top" align="left" width="320">Aperture, magnification, manual
      focus</td>
    <td valign="top" align="left" width="270">Shutter speed or <a href="#iso">ISO</a></td>
  </tr>
  <tr>
    <td valign="top" align="left" width="175"><a href="#shake">Steadiness</a></td>
    <td valign="top" align="left" width="320">Shutter speed, magnification, <a href="#support">
      support</a></td>
    <td valign="top" align="left" width="270">Aperture or <a href="#iso">ISO</a></td>
  </tr>
  <tr>
    <td valign="top" align="left" width="175"><a href="#stop-action">Stop-action</a></td>
    <td valign="top" align="left" width="320">Shutter speed, magnification</td>
    <td valign="top" align="left" width="270">Aperture or <a href="#iso">ISO</a></td>
  </tr>
  <tr>
    <td valign="top" align="left" width="175"><a href="#dynamic">Dynamic range</a></td>
    <td valign="top" align="left" width="320"><a href="#spot">Spot metering</a>,
      <a href="#fill"> fill flash</a>, special <a href="filters.htm"> filters</a>&nbsp;</td>
    <td valign="top" align="left" width="270">Subject vs. highlight vs. shadow <a href="#tonality">tonalities</a>&nbsp;</td>
  </tr>
</table>
<p>To make things a bit more concrete, the discussions below are cast in terms of the camera I know
best�the highly malleable 2.1 megapixel Oly C-2020Z. However, the same considerations readily transfer to
any digital camera with similar controls and features, including the Oly C-30x0Z.</p>
<hr>
<h3><b><a name="monitoring"></a>Monitoring Exposure</b></h3>
<p><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;Your camera
can teach you a lot if you check its exposure display early and often. If you shoot without
checking the consequences of your settings, you may not get what you bargained
for.&nbsp;Take a moment to frame a
test shot and see the camera's take on
what you're about to do, particularly when pushing the exposure envelope.</p>
<p> In all metering modes on the C-2020Z, a half-press of the shutter release with the main (rear) LCD
turned on will display the setting(s) you're controlling in green and any settings left to the
camera's discretion in white. If the setting(s) you're in charge of turn red, you've brought the camera to its
knees�for example, by setting a fast shutter speed in shutter priority mode in
low light requiring an f/1.4 aperture when f/2 is the widest the
camera can deliver. In all modes but auto, the C-2020Z goes on to underline the offending red setting(s)
and beneath that shows an up or down arrow corresponding to the exposure control
button you need to use to return to the camera's recommended exposure.</p>
<p>In <i>aperture- and shutter-priority modes</i>, this simple check will show you what the camera's
coming up with for the setting left to its control�e.g., shutter speed in aperture-priority
mode. If the camera's choice in a priority mode proves inconsistent with your goals for the shot at
hand, you'll have to&nbsp;</p>
<ul>
  <li> rethink the setting you're controlling,</li>
  <li> override the camera with an <a href="#ec"> exposure compensation</a> (EC) adjustment,
    or</li>
  <li>take your chances with manual exposure.</li>
</ul>
<p>In <i>manual mode</i>, checking the exposure display will show you whether the
camera's looking or more or less light or is content with the <a href="#ev">EV</a>
corresponding to your choices.</p>
<p> Even <i> program mode</i> displays its choices with that
half-press of the shutter button, but I seem to catch on faster when forced to
commit to at least part of the exposure decision.</p>

<div align="left">
  <table border="0" cellspacing="0" cellpadding="0">
    <tr>
      <td valign="bottom"><a href="index.htm#site_index"><img border="0" src="art_index.gif" width="133" height="34"></a></td>
      <td valign="bottom"><a href="#page_index"><img border="0" src="up.gif" width="41" height="51"></a></td>
      <td valign="bottom"><a href="filters.htm"><img border="0" src="next_art.gif" width="133" height="34"></a></td>
    </tr>
  </table>
</div>

<hr>

<h2><b><a name="recording"></a>Recording
Mode�Critical Pre-Exposure Digital Decisions</b></h2>

<p>Before you even get to an actual exposure, you'll need to set up an
appropriate <i>recording mode</i> for your digital camera. Involved are no less
than 6
fundamental and largely independent camera settings, each representing an important
decision with very real consequences. For the most part, these decisions will be
unfamiliar from your film experience, but they're critical nonetheless. The
table below summarizes the recording mode settings and the issues at stake.</p>

<table border="2" width="818">
  <tr>
    <td valign="top" align="left" width="1074" colspan="4">
      <h4><b>Recording Mode Options</b></h4>
    </td>
  </tr>
  <tr>
    <td valign="top" align="left" width="147"><b>Setting</b></td>
    <td valign="top" align="left" width="274"><b>Basic Trade-offs</b></td>
    <td valign="top" align="left" width="373"><b>At Stake</b></td>
    <td valign="top" align="left" width="373"><b>Best Bet</b></td>
  </tr>
  <tr>
    <td valign="top" align="left" width="147">

<p><a href="#iso">ISO</a></p>

    </td>
    <td valign="top" align="left" width="274">
      <ul>
        <li><a href="#noise">Image noise</a></li>
        <li>Effective light sensitivity</li>
      </ul>
    </td>
    <td valign="top" align="left" width="373">
      <ul>
        <li>Image quality</li>
        <li>Exposure, especially in <a href="#stop-action">action shots</a></li>
      </ul>
    </td>
    <td valign="top" align="left" width="373">Minimum available ISO whenever
      feasible</td>
  </tr>
  <tr>
    <td valign="top" align="left" width="147">

<a href="#color_mode">Color Mode</a>

    </td>
    <td valign="top" align="left" width="274">
      <ul>
        <li>Convenience</li>
        <li>Archiving, post-processing and printing options, especially in <a href="bandw.htm">B&amp;W</a>
          work&nbsp;</li>
      </ul>
    </td>
    <td valign="top" align="left" width="373">
      <ul>
        <li>Image quality</li>
        <li>In non-color modes, downstream availability of a full color
          version&nbsp;</li>
      </ul>
    </td>
    <td valign="top" align="left" width="373">Full color recording</td>
  </tr>
  <tr>
    <td valign="top" align="left" width="147">

<p><a href="#resolution">Resolution</a></p>

    </td>
    <td valign="top" align="left" width="274">
      <ul>
        <li>Pixel count</li>
        <li>File size</li>
      </ul>
    </td>
    <td valign="top" align="left" width="373">
      <ul>
        <li>Image quality</li>
        <li>Post-processing and printing options</li>
        <li><a href="#memory">Memory card capacity</a></li>
        <li><a href="#latency">Shot-to-shot latency</a></li>
      </ul>
    </td>
    <td valign="top" align="left" width="373">Maximum available resolution
      whenever feasible</td>
  </tr>
  <tr>
    <td valign="top" align="left" width="147">

<p><a href="#compression">Compression Level and Color Interpolation</a>&nbsp;&nbsp;</p>

    </td>
    <td valign="top" align="left" width="274">
      <ul>
        <li><a href="#jpeg_artifacts">JPEG artifacts</a></li>
        <li>File size</li>
        <li>Post-processing options</li>
      </ul>
    </td>
    <td valign="top" align="left" width="373">
      <ul>
        <li>Same as with resolution, but with
      less adverse impact on quality and options.</li>
        <li>Ability to select white balance in post-processing</li>
      </ul>
    </td>
    <td valign="top" align="left" width="373"><a href="#testing">Test</a> to see
      what works for you</td>
  </tr>
  <tr>
    <td valign="top" align="left" width="147"><a href="#sharpening">Sharpening</a></td>
    <td valign="top" align="left" width="274">
      <ul>
        <li>In-camera convenience</li>
        <li>Post-processing flexibility</li>
      </ul>
    </td>
    <td valign="top" align="left" width="373">
      <ul>
        <li>Image quality</li>
        <li>Post-processing and printing options</li>
      </ul>
      <p>&nbsp;</td>
    <td valign="top" align="left" width="373"><a href="#testing">Test</a> to see
      what works for you</td>
  </tr>
  <tr>
    <td valign="top" align="left" width="147"><a href="#wb">White Balance</a></td>
    <td valign="top" align="left" width="274">
      <ul>
        <li>None</li>
      </ul>
    </td>
    <td valign="top" align="left" width="373">
      <ul>
        <li>Color balance</li>
      </ul>
    </td>
    <td valign="top" align="left" width="373">Auto works well <i>most</i> of the
      time</td>
  </tr>
</table>

<p>I think of these 6 settings together as my <i>recording mode</i>. The only
one tied directly to exposure is <a href="#iso">ISO</a>, of course, but the
others deserve mention in this context because...</p>

<table border="0">
    <tr>
        <td valign="top"><a href="index.htm#warranty"><em><strong><img src="tumbling_arrow.gif" alt="Marks the gotchas" align="left" border="0" hspace="0" width="16" height="16"></strong></em></a></td>
        <td valign="top"><i><b>Inappropriate recording mode choices
          can easily and irreversibly introduce noise and artifacts into your images
          and can severely limit your post-processing and printing options down
          the line.&nbsp;</b></i></td>
    </tr>
</table>

<p>Before taking your first serious digital photograph, it would be a good idea
to work through the 6 absolutely irreversible recording mode issues�<a href="#iso">ISO</a>,
<a href="#color_mode">color mode</a>, <a href="#resolution">resolution</a>,
<a href="#jpeg">compression and color interpolation</a>  and <a href="#sharpening">sharpening</a>�preferably by <a href="#testing"> testing</a> to find what meets your needs. Let the most demanding <i> credible</i> end-uses for
your images be your guides. (Remember, digital cameras make testing easier and cheaper than ever before.)
Fortunately, you can often fix <a href="#wb">white balance</a> problems in
post-processing�especially when the scene contains something that really is
white.</p>

<table border="0">
    <tr>
        <td valign="top"><em><strong><a href="#resolving"><img src="bypass.gif"
        alt="Marks opportunities to bypass long-winded discussions and cut to the action line. Click to review Limited Warranty section on the home page."
        align="texttop" border="0" width="36" height="30"></a></strong></em></td>
        <td valign="top">Click at left to skip to <a href="#resolving">resolving
          power</a> now. To review the elements of recording mode one by one, read on.</td>
    </tr>
</table>

<hr>
<h3><a name="color_mode"></a>Color Mode</h3>
<p>This one's simple.&nbsp;</p>
<blockquote>
  <p><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>       <b>Record
  in full color unless there's an overwhelming reason to do otherwise.</b></p>
</blockquote>
<p>Recording exclusively in B&amp;W (grayscale), sepia, blackboard and other
special in-camera recording modes <i>severely</i> limits all your downstream
options with those images. If you have the time, the skill and the right tools,
these effects can <i>always</i> be achieved in post-processing, usually with <i>much</i>
better results. That's especially true in <a href="bandw.htm">B&amp;W work</a>.</p>
<p>If you lack the post-processing resources or otherwise prefer to record in,
say, B&amp;W or sepia mode, I strongly recommend taking and archiving a full
color exposure as well. Whatever you do,</p>

<table border="0">
    <tr>
        <td valign="top"><a href="index.htm#warranty"><em><strong><img src="tumbling_arrow.gif" alt="Marks the gotchas" align="left" border="0" hspace="0" width="16" height="16"></strong></em></a></td>
        <td valign="top"><i><b>Don't forget to restore full color recording
          after using other modes.</b></i></td>
    </tr>
</table>

<hr>

<h3><a name="iso"></a><b>Digital ISO Settings</b></h3>

<p>The <i> ISO setting</i>  on a digital camera determines its overall light
sensitivity, just as the ISO rating on a film canister informs the photographer
of the sensitivity of the film inside. The ability to change light sensitivity
at will <i>without physically swapping out the image receiver</i> is one of the
more important benefits of digital recording. Of course, digital and film light
sensitivities arise from vastly different physical processes, but digital camera
engineers work hard to align their ISO settings with established film ISO
ratings to preserve the applicability of tried-and-true exposure
expectations like the <a href="#sunny">sunny f/16 rule</a>. After all, forcing
experienced photographers to relearn exposure on moving to the digital side is
no way to sell digital cameras.</p>

<p>The manual for my Oly C-2020Z states,</p>
<blockquote>
  <p>The sensitivity [ISO] scale is based on the one used for
  picture film, but the numbers are for reference only.</p>
</blockquote>
<p>In other words, exact equivalence with film speed (ISO) isn't guaranteed, but
for any given scene at any given ISO, the C-2020Z and film will require about the same light input
or <a href="#ev">EV</a>.</p>
<p>How close the equivalence comes probably varies from camera to camera (mine
acts more like ISO 80 when set to ISO 100, as discussed <a href="#iso_actual">below</a>), but the potential
for discrepancy is by no means unique to the digital side. The true ISO of a given
camera-film combination doesn't always match the nominal ISO of the film used.
For
precision work with external light meters, professionals usually find it
necessary to calibrate the true ISO of each different camera-film combination
they use. Digital cameras are no different.</p>

<h4><a name="noise"></a><b>Noise</b></h4>

<p>The big difference between digital ISO and film ISO relates to image noise,
which is only partly analogous to film grain. To be sure, image noise increases
predictably with increasing ISO, just a film grain does, and noise can sometimes
look like grain, but once it becomes visible, noise is much more an image flaw
than grain. Furthermore, noise can be manipulated in ways that grain can't.</p>

<p>To simplify the discussion that follows, I've extended the concept of <i> noise</i> beyond the realm of random time-varying
phenomena to include more deterministic but equally undesirable image artifacts
like those due to <a href="#dcn"> dark current</a>. (No one wants it in their images, but some technically-minded visitors
don't consider dark current artifacts true noise. I won't get into
that debate here.)</p>

<p>In digital photography, the noise of practical interest comes in two
flavors�<a href="#rn">random</a> and <a href="#fpn">fixed-pattern</a>�differing
somewhat in cause and remedy. Both types tend to be most problematic in low-light situations.</p>

<p><b><a name="rn"></a>Random Noise</b></p>

<p><i>Random noise</i> (RN) arises from&nbsp;</p>

<ul>
  <li>
    <p style="margin-bottom: 9">primarily thermal
fluctuations in the electronic components that handle the analog CCD output signal</li>
  <li>
    <p style="margin-bottom: 9">quantum (statistical) fluctuations in the numbers of photons reaching
    CCD sensels from the scene&nbsp;</li>
</ul>

<p> RN varies unpredictably, both in time and across the image
frame. Since RN is uncorrelated, it can be reduced effectively by <a href="c-2000z/low-light/index.htm#averaging">image
averaging</a>, a technique well known to CCD astronomers, professional and
amateur alike. For every N identical exposures averaged together, the RN-related
signal-to-noise ratio increases by a factor of sqrt(N).</p>

<p><i><a href="images/rn.jpg"><img border="0" src="images/rn0.jpg" alt="Low-light view of San Francisco Bay showing random noise in dark areas. Click to see 800x600 version. [C-2020Z]" align="right" width="160" height="120"></a></i><a name="cooling"></a>RN is aggravated by underexposure,
by high CCD
temperatures and by physically small sensels. It produces a speckled pattern in affected images, often most
conspicuously in the shadows, as seen in the example at right. (The best
appreciate the noise, view the full size image at 400% magnification.)</p>

<p>To minimize RN, avoid underexposure, keep ISO at
the minimum feasible setting and keep your camera cool. If you plan to shoot
outside on a cold night, let the camera equilibrate with the cool air
beforehand. (Cooling your camera below ambient temperature will invite
condensation on the lens and elsewhere, possibly damaging the camera.) Some go
so far as to avoid LCD use to keep their LCDs from heating the CCDs nearby, but
I have yet to see a compelling case for this practice. If you decide to take
several redundant exposures for <a href="c-2000z/low-light/index.htm#averaging">averaging</a>
in post-processing, record them a <i>lossless</i> (TIFF or
RAW) format and use a sturdy tripod and a remote shutter release to eliminate
any possible camera shake.</p>

<p><b><a name="fpn"></a>Fixed-Pattern Noise</b></p>

<p><i>Fixed-pattern noise</i> (FPN) varies in time but is rooted in
inhomogeneities among the CCD sensels and thus exhibits a fixed pattern across
the image frame.</p>

<p><i><a name="dcn"></a>Dark current noise</i> (DCN), the most commonly visible
form of FPN, results when stray electrons leak into sensels from the surrounding
substrate in the absence of incoming light. Some sensels leak faster than
others, and the longer the exposure and the hotter the CCD, the more dark
current electrons a given sensel will accumulate. In low light, dark current
electrons may even outnumber the photoelectrons liberated by gathered photons in
the leakiest sensels. At constant temperature and exposure time, each sensel's
dark current electron load varies randomly about a mean. A <i>dark frame</i>
exposed with no light input (e.g., with a lens cap on) will show the
instantaneous dark current pattern for a specific temperature and exposure time.
An average of several time- and temperature-matched dark frames will approach
the mean dark current pattern. Within limits, you can reduce DCN by <a href="c-2000z/low-light/index.htm#dark_current">subtracting
dark currents</a> from an image, preferably with an average of several dark
frames, as CCD astronomers often do, but you will add some RN in the process.&nbsp;</p>

<div align="left">
  <table border="2">
    <tr>
      <td colspan="2">
        <h4>Fixed-Pattern Noise in a Cold 4-Second Exposure</h4>
      </td>
    </tr>
    <tr>
      <td rowspan="4" valign="top" align="left">DCN is aggravated by high CCD temperatures, by long exposures and by CCD
aging. It produces an array of scattered abnormally bright (&quot;hot&quot; or
&quot;warm&quot;) pixels in affected images, again most conspicuously in the
        shadows, as seen at right.&nbsp;
        <p>This 4-second image of the crescent moon and Mercury (top right
        corner) and its matching dark frame were recorded back-to-back with the
        camera thermally equilibrated with the cold night air. The dark frame
        won't do for subtraction (try it and see) because it was recorded in a
        lossy (<a href="#jpeg">JPEG</a>) format.</td>
      <td><i><a href="images/fpn.jpg"><img border="0" src="images/fpn0.jpg" alt="Long (4 sec) exposure of the crescent moon and Mercury showing fixed pattern noise.. Click to see 800x600 version. [C-2020Z]" align="right" width="160" height="120"></a></i></td>
    </tr>
    <tr>
      <td>
        <p align="center"><b>4 sec Scene</b></td>
    </tr>
    <tr>
      <td><i><a href="images/fpn_dark_frame.jpg"><img border="0" src="images/fpn_dark_frame0.jpg" alt="Long (4 sec) dark frame showing fixed-pattern noise.. Click to see 800x600 version. [C-2020Z]" align="right" width="160" height="120"></a></i></td>
    </tr>
    <tr>
      <td>
        <p align="center"><b>Dark Frame</b></td>
    </tr>
  </table>
</div>
<p> To minimize DCN, avoid exposures over 1/2 sec and keep your camera
cool as explained <a href="#cooling">above</a>. If you decide to take several
redundant dark frames for averaging and <a href="c-2000z/low-light/index.htm#dark_current">subtraction</a>
in post-processing, record them in a <i>lossless</i> (TIFF or
RAW) format on location, taking care to match the CCD temperature and exposure
time of the target image. Be sure to use a sturdy tripod and a remote shutter
release to eliminate any possible camera shake.</p>

<p><b>Gray Frames</b></p>

<p>Another source of FPN less important in digital photography is variability in
sensitivity (the proportionality between captured photon count and output
voltage) among sensels. This fixed inhomogeneity can be corrected by shooting a
known uniform target several times to obtain an average <i>gray field.</i>
Dividing the image at hand by the gray field normalizes sensitivity across the
CCD.</p>

<p><b>All-Out Noise Abatement</b></p>

<p>The full court press against noise in post-processing involves the averaging
of several redundant images, division of that average by a gray frame and
finally, the subtraction of the average of several dark frames, all recorded in
a lossless format.</p>

<h4><b>ISO, Amplification, Analog-to-Digital Conversion and Noise</b></h4>
<p>Digital cameras adjust their light sensitivity (ISO) in two ways:</p>

<ul>
  <li>
    <p style="margin-bottom: 9">By varying the amplification applied to the CCD's analog output
    signal before analog-to-digital (A/D) conversion</li>
  <li>
    <p style="margin-bottom: 9">By remapping ~12 bits worth of analog CCD output
    onto 8 bits of digital output in the camera's A/D converter (ADC)</li>
</ul>
<p>Hybrid approaches are probably common here, but either way, the noise inevitably present
in the CCD's analog output gets amplified, electronically or mathematically, right along with the signal,
and the pre-ADC amplifier adds further noise of its own. Increased sensitivity
comes at the price of increased noise, period.&nbsp;</p>

<p>For every doubling of ISO, the light
input required for a proper exposure drops by a full <a href="#stops"> stop</a>
(a factor of 2), while image
signal-to-noise ratio (SNR) drops by a factor of 1/sqrt(2) = 71%.
Conversely, the required light input increases by 2 stops and SNR doubles in
going from ISO 400 to ISO 100 at constant image brightness.
The table below shows the quantitative relationship between ISO and time-varying
<a href="#rn"> random noise</a> at constant image brightness.&nbsp;</p>

<div align="left">
  <table border="2">
    <tr>
      <td valign="top" align="left">
        <h4><b>ISO Setting&nbsp;</b></h4>
      </td>
      <td valign="top" align="left">
        <h4><b>Relative Signal-to-Noise Ratio&nbsp;</b></h4>
      </td>
      <td valign="top" align="left">
        <h4><b>Relative Random Noise Level&nbsp;</b></h4>
      </td>
    </tr>
    <tr>
      <td align="right" valign="top">100</td>
      <td align="right" valign="top">1.00</td>
      <td align="right" valign="top">100%</td>
    </tr>
    <tr>
      <td align="right" valign="top">200</td>
      <td align="right" valign="top">0.71</td>
      <td align="right" valign="top">141%</td>
    </tr>
    <tr>
      <td align="right" valign="top">400</td>
      <td align="right" valign="top">0.50</td>
      <td align="right" valign="top">200%</td>
    </tr>
  </table>
</div>

<p>To make matters worse, <a href="#rn"> random
noise</a> and fixed-pattern <a href="#dcn">dark current noise</a>
 <i>
 both</i> increase with increasing ISO in CCD-based imaging devices. Long multi-second exposures tend to run afoul of
<a href="#dcn">dark current noise</a>, even at minimum ISO, and higher ISO settings only compound the problem. See the <b>dp<i>FWIW</i></b> article <a
href="c-2000z/low-light/index.htm">Low-light work
with the C-20x0Z</a> for details on long exposures with digital cameras.</p>
<h4><b>Using ISO Wisely</b></h4>
<p>Controlling exposure by manipulating ISO <i>in lieu of</i> aperture or
shutter speed is generally a bad idea because higher ISO settings beget more <a href="#noise">image
noise</a>, as we've just seen. But ISO adjustments are often inescapable in <a href="#stop-action">stop-action</a>
work, where short exposures and low available light are a common mix.&nbsp;</p>
<p>The increased noise isn't always subtle, but if a higher ISO makes a
must-have shot possible, the noise may well be a price worth paying. Image noise tends to
be more apparent in the shadows (which may be expendable) and at higher final magnifications, like the ones
needed for 8x10 prints (which may not be needed). With forethought and extra exposures specifically
designed for the purpose, you can significantly mitigate noise in
post-processing in relatively <i>static</i> scenes like the night sky sans <a href="moon.htm">moon</a>, but
such <a href="c-2000z/low-light/index.htm#dark_field">subtraction</a> and <a href="c-2000z/low-light/index.htm#averaging">averaging</a>
 techniques aren't applicable to the short exposures needed for <a href="#stop-action">stop-action
work</a>, where need to bump ISO issue most often arises.</p>

<p>The safest ISO policy is this:&nbsp;</p>

<table border="0">
    <tr>
        <td valign="top"><a href="index.htm#warranty"><em><strong><img src="tumbling_arrow.gif" alt="Marks the gotchas" align="left" border="0" hspace="0" width="16" height="16"></strong></em></a></td>
        <td valign="top"><b><i>Bump ISO only as a last resort and never more
          than absolutely necessary.</i></b></td>
    </tr>
</table>

<p>If you dial in a high ISO for a specific purpose, make sure you set it back
to your camera's minimum before you forget.</p>

<p>Note that some large-sensor cameras like the Nikon D1x and the Canon D30 and
D60 deliver very acceptable noise levels at ISO 400 and beyond, but be prepared
to shell out big money for that kind of low-light performance.</p>

<h4><a name="auto-iso"></a>Beware Auto-ISO</h4>

<p>BTW, keep an eye on ISO in low-light situations in auto-exposure mode. Some
cameras like my
old C-2000Z take liberties with ISO under such conditions, even though a specific
ISO has been set in the menus. Since the C-2000Z otherwise respected my ISO setting, I nearly always
used it in aperture- or shutter-priority modes to lock in ISO 100. Thankfully, the C-2020Z
and later Oly digitals offer more predictable ISO control options alongside an
auto-ISO setting.</p>

<table border="0">
    <tr>
        <td valign="top"><a href="index.htm#warranty"><em><strong><img src="tumbling_arrow.gif" alt="Marks the gotchas" align="left" border="0" hspace="0" width="16" height="16"></strong></em></a></td>
        <td valign="top"><b><i>Action photography aside, avoid auto-ISO settings
          like the plague.</i>&nbsp;</b></td>
    </tr>
</table>

<hr>

<h3><b><a name="resolution"></a>Image Resolution</b></h3>

<p>Pixel count is by far the single most important determinant of image quality
in digital photographs, particularly when it comes to printing, and <i>resolution</i>
(e.g., 1600x1200 vs. 800x600) determines pixel count. The higher the resolution,
the more pixels you'll capture and the better the image you'll have. A 1600x1200 image
contains 4 times the pixels of an 800x600 version and will be commensurately sharper and less &quot;pixelly&quot;
at any given print or display size. A 1600x1200 <a href="#jpeg">JPEG</a>
compressed at 4:1 will
contain about as many bytes as its uncompressed 800x600 counter part, but the
1600x1200's quality will
almost always be conspicuously superior to the 800x600's at such mild
compression levels.&nbsp;In a very real sense, reduced resolution is the crudest
possible form of &quot;compression&quot;, with results to match.</p>

<p>That makes the resolution decision pretty easy:</p>

<blockquote>

<p><b><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;Record at
your camera's maximum resolution whenever feasible.</b></p>

</blockquote>
<p>If you still need convincing, read <a href="http://www.wfu.edu/~matthews/misc/graphics/ResVsComp/JpgResVsComp.html">Higher
resolution or lower compression JPEGs?</a> by <b>dp<i>FWIW</i></b> contributor
and physicist <a href="index.htm#matthews">Rick Matthews</a>. Rick's
illustrations say it all.&nbsp;</p>

<p>To avoid the hassle of downsizing images after the fact, some users record
images destined for Web use or e-mails to friends at lower resolutions. But what
happens when you end up wanting to print an unexpectedly good one at 8x10? Cropping, downsampling and other pixel-wasting operations are best left for
post-processing with a specific end-use in mind, and many editors now offer
batch processing and macros to automate such tasks. (If you're unfamiliar
with these manipulations and the issues they entail, be sure to read <a href="http://homepage.dtn.ntl.com/j.houghton/images.htm">John
Houghton's excellent image sizing primer</a>.)</p>

<p>Bottom line: At exposure time, grab all the pixels
you can because...</p>

<table border="0">
    <tr>
        <td valign="top"><a href="index.htm#warranty"><em><strong><img src="tumbling_arrow.gif" alt="Marks the gotchas" align="left" border="0" hspace="0" width="16" height="16"></strong></em></a></td>
        <td valign="top"><b><i> Inappropriate
resolution choices can severely limit your post-processing and printing
options down the line.</i></b></td>
    </tr>
</table>

<h4><b><a name="memory"></a>Memory Allocation</b></h4>

<p>Memory card capacity is by far the most important limiting factor here,
but&nbsp; recording at full resolution is your <i>single most effective
allocation</i> of that valuable resource. Since a 4-to-1 drop in resolution
(e.g., from 1600x1200 to 800x600) is
usually much more detrimental than a 4:1 <a href="#jpeg">JPEG compression</a>, judicious use of <a href="#compression">compression</a>
can more than offset the memory hit that comes with increased
resolution�typically with far less impact on image quality and post-processing
and printing options.&nbsp;</p>

<h4><b><a name="latency"></a>Shot-to-Shot Latency</b></h4>

<p>Many factors affect the time lag between one shot and the next in a digital
camera. <i>File write time</i>, the time required to store an image on a memory card
once the camera's processed it, is usually the rate-limiting step in getting to
the steady green light for the next shot. Write time increases roughly linearly with
pixel count and therefore with resolution. In-camera processing times increase
with higher resolutions as well. Even though <a href="#compression">compression</a>
itself adds to the processing time, judicious use of <a href="#compression">compression</a>
can more than offset the time increased resolution adds to your camera's
shot-to-shot latency. In theory, <a href="#sharpening">in-camera sharpening</a>
also adds to latency, but I haven't noticed the difference if it does.&nbsp;&nbsp;</p>

<hr>

<h3><b><a name="compression"></a>Image Compression and Color
Interpolation</b></h3>

<p>Digital image files are inherently large. The true-color (24-bit) images
produced by most cameras take up 3 bytes per pixel. With EXIF header
information, that comes to 5.5MB for a 1600x1200 image from a lowly 2 megapixel
camera!</p>

<p>One way to reduce image files to more manageable sizes is to apply <a href="#compression">compression</a>. With smaller files, you can fit a larger number of images or images
of higher <a href="#resolution">resolution</a> on a single memory card. Another
way is to record only raw CCD data in-camera, leaving color interpolation and
expansion into RGB triples for post-processing. Cameras offering <a href="#raw">RAW
recording</a> also give you the option of performing color interpolation and
white balance adjustments in post-processing on a computer with a lot more
resources than the one in the camera.</p>

<p>Of course, <a href="#compression">compression</a> and <a href="#raw">RAW
recording</a> aren't exposure issues per se, but like other recording mode settings,
they're certainly worth addressing
before embarking on serious work with a digital camera.</p>

<h4><b><a name="jpeg"></a>JPEG Compression</b></h4>

<p>Nearly all digital cameras offer image recording with the lossy but highly effective JPEG (Joint Photographic Experts Group)
compression scheme. The JPEG standard was explicitly designed to compress
photographs and other <i> continuous-tone images</i> in accordance with the <a href="vision.htm#brain-eye"> brain-eye
system</a>'s well-known ability to detect smaller changes in intensity
(luminance) than in color (chrominance). In other words, JPEG compression favors the retention of luminance over chrominance
data.</p>

<p>JPEG does this very well, but there's a catch: As with any lossy compression
scheme, the greater the compression, the smaller the final file size but the greater the data loss, and the more apparent the compression damage when the
image is re-expanded. The compression damage takes many forms, all lumped under
the term <i><a href="#jpeg_artifacts">JPEG artifacts</a></i>.&nbsp;</p>

<p>By design, JPEG compression is poorly suited to line drawings and text. GIF
and <a href="http://www.libpng.org/pub/png/"> PNG</a> are the compression schemes of choice for such images.</p>

<p>Choosing an appropriate JPEG compression level amounts to making the best
trade-off between image quality and final image file size based on your most
stringent credible end-use for the images at hand. Only you can make that call
based on testing with your own equipment.</p>

<p> The coming
JPEG2000 update of the current JPEG standard promises to do a much better job with
wavelet technology, but few cameras now in use will be able to take advantage of
it.&nbsp;</p>

<p>You can learn more about JPEG compression from this excellent <a href="http://www.faqs.org/faqs/jpeg-faq/part1/">JPEG
FAQ page</a>.&nbsp;</p>

<h4><b><a name="jpeg_artifacts"></a>JPEG Artifacts
and Compression Levels</b></h4>
<p><i>JPEG artifacts</i>  are unwelcome image features arising directly from
damage done to the original image data during compression and re-expansion. The smaller
the final compressed file size, the greater the damage will be and the more
conspicuous the
JPEG artifacts will become.</p>

<div align="left">
  <table border="0">
    <tr>
      <td valign="top" align="left"><img border="0" src="images/jpeg_artifacts.jpg" alt="Heavily compressed JPEG test image, courtesy John Houghton." width="622" height="450"></td>
    </tr>
    <tr>
      <td valign="top" align="left"><a href="http://homepage.dtn.ntl.com/j.houghton/images.htm">John
        Houghton</a> kindly supplied this heavily compressed illustration of
        common JPEG artifacts. Note the ripples along the margins of the red
        square, the blocky transitions in the blue gradient background and the
        ringing around the text and the red square.</td>
    </tr>
  </table>
</div>

<p>Now that you've come face to face with JPEG artifacts, you're probably
wondering if the &quot;maximum resolution, compressing as needed&quot; strategy
touted <a href="#resolution">above</a> is really all that smart. Once again, I
invite you to see for yourself at <a href="http://www.wfu.edu/~matthews/misc/graphics/ResVsComp/JpgResVsComp.html">Higher
resolution or lower compression JPEGs?</a> by <b>dp<i>FWIW</i></b> contributor
and physicist <a href="index.htm#matthews">Rick Matthews</a>. &nbsp;</p>

<p><b><a name="worst"></a>Worst Case Scenarios</b></p>

<p>Very sharp, high-contrast boundaries like those in line
drawings and text show obvious rippling and ringing at almost any JPEG compression level.
Such boundaries represent the very worst case JPEG scenario, but luckily, they
aren't all that common in photographs. (That's why they weren't a priority for
JPEG designers.)</p>

<p>In routine photographs, JPEG artifacts are most likely to show up as subtle bandings within large
low-contrast areas like the sky or as speckles or ripples along color
boundaries, particularly diagonal ones.&nbsp;Images with rapid color changes
over very short distances also suffer to some extent under JPEG
compression.&nbsp;</p>

<p>The less image detail, the higher the image quality for a given JPEG
compression ratio.
In highly detailed scenes with lots of color changes from pixel to pixel, the
space actually saved with a given compression level will be greatly reduced.&nbsp;</p>

<p><b>See For Yourself</b></p>

<p>To see the damage for yourself, copy some challenging images from your
collection based on the guidelines <a href="#worst">above</a>, compress the living daylights out of
the copies, and then zoom in on the resulting images. Then back off on the
compression level to see where the most noxious artifacts first appeared.</p>

<h4><b>JPEG Options</b></h4>

<p>Most digital cameras allow you to set the level of <a href="#jpeg">JPEG compression</a> applied, and many now
allow you turn it off completely. As with <a href="#resolution">resolution</a>,
image quality, post-processing and printing options, <a href="#memory">memory
card capacity</a> and <a href="#latency">shot-to-shot latency</a> all hang in
the balance. Your willingness to change cards frequently enters the equation
when compression is disabled, even with large cards.</p>

<p> The compression options in the table below are typical of
higher-end cameras.&nbsp;&nbsp;</p>

<div align="left">
  <table border="2" width="863">
    <tr>
      <td valign="top" align="left" width="396"><b>Oly C-2020Z Compression Options&nbsp;</b></td>
      <td colspan="3" valign="top" align="left" width="415"><b>Average Image File
        Statistics</b></td>
    </tr>
    <tr>
      <td valign="top" align="left" width="396">Compression Level (recording
        option, file format)</td>
      <td valign="top" align="left" width="158">File Size (KB) at&nbsp; 1600x1200</td>
      <td valign="top" align="left" width="138">Nominal Compression Ratio</td>
      <td valign="top" align="left" width="141">Images Per 32MB Card</td>
    </tr>
    <tr>
      <td valign="top" align="left" width="396">None (SHQ, TIFF)</td>
      <td valign="top" align="right" width="158">5,500</td>
      <td valign="top" align="right" width="138">1:1</td>
      <td valign="top" align="right" width="141">5</td>
    </tr>
    <tr>
      <td valign="top" align="left" width="396">Light (SHQ, JPEG)</td>
      <td valign="top" align="right" width="158">1,400</td>
      <td valign="top" align="right" width="138">4:1</td>
      <td valign="top" align="right" width="141">22</td>
    </tr>
    <tr>
      <td valign="top" align="left" width="396">Medium (HQ, JPEG)</td>
      <td valign="top" align="right" width="158">400</td>
      <td valign="top" align="right" width="138">14:1</td>
      <td valign="top" align="right" width="141">64</td>
    </tr>
  </table>
</div>
<h4><b>RAW and TIFF Recording</b></h4>
<p>To avoid JPEG artifacts in your captured images, you'll have to turn to an
output file format using either lossless compression or no compression at all.
That's where <a href="#raw">RAW</a> and <a href="#tiff">TIFF</a> recording come
in, but be prepared to pay a hefty price in&nbsp;</p>
<ul>
  <li>
    <p style="margin-bottom: 9">drastically reduced memory card capacity in
    terms of images per card</li>
  <li>
    <p style="margin-bottom: 9">drastically increased <a href="#latency">shot-to-shot
    latencies</a> via extended file write times</li>
  <li>
    <p style="margin-bottom: 9">prolonged download times from the camera,
    and&nbsp;</li>
  <li>
    <p style="margin-bottom: 9">with RAW files, extra and prolonged initial
    post-processing steps.</li>
</ul>
<p>For some photographers, or for some shots, the TIFF or RAW cost/benefit ratio
may make perfect sense,
but the fact of the matter is that most digital photographers record JPEGs most
of the time.</p>
<p><a name="raw"></a><b>RAW Recording</b></p>
<p>RAW output files contain digitized but otherwise raw sensor data without color
interpolation, <a href="#wb">white balance</a> adjustment or <a href="#sharpening">
sharpening</a>. In many ways, they represent a &quot;digital negative&quot; and
are sometimes referred to as such. Professionals strongly favor RAW recording
because it maximizes both post-processing flexibility <i> and</i> final image
quality for reasons explained <a href="#raw_advantages">below</a>. Unfortunately, you won't be able to view or
edit RAW images straight from the camera with any old image viewer or editor. RAW formats are still quite camera-specific.
To convert RAW images to something you can actually work with, you'll have to
rely on the proprietary software supplied with your camera. Worse yet, RAW conversions are
often quite slow, even on fast computers.&nbsp;</p>
<p><a name="raw_advantages"></a>What are the RAW advantages? For starters, RAW recording allows you to
&quot;externalize&quot; certain basic processing tasks better performed outside
the camera. In-camera color interpolation, white balance and sharpening algorithms have to make
significant compromises in order to keep <a href="#latency">shot-to-shot latencies</a>
reasonable while working within camera limitations revolving around CPU speed,
available RAM and allowable firmware footprint. If you'd rather not be subject to
such compromises, RAW recording may be the ticket�if your camera offers it.&nbsp;</p>
<p>
External color interpolation, white balance and sharpening algorithms running on
a desktop or notebook computer can afford to be much
more sophisticated (read &quot;more CPU- and memory-intensive&quot;).&nbsp;
External algorithms are also free to take their own sweet time since no one's
champing at the bit to squeeze off the next shot (although they may well be
waiting to get on with their editing). Another RAW advantage is the
ability to adjust <a href="#wb">white balance</a> after the fact. Although RAW files
are typically quite a bit larger than the least compressed JPEGs offered,
they're <i>usually</i> significantly smaller than the corresponding TIFFs. To
make their RAW files even smaller, some cameras, like the Nikon D1x, offer
(presumably lossless) RAW compression.</p>
<p>Less widely appreciated is the <b>greater dynamic range</b> afforded by RAW
recording. RAW sensor data is typically digitized at 10-12 bits per sensel, but
JPEG and TIFF images must be requantized to 8 bits per primary color channel
during color interpolation. Reduced bit-depth and associated quantization errors
mean more blown-out highlights and black-hole shadows, among other artifacts. By
post-processing at the higher RAW bit-depth and <i>then</i> saving to an 8 bit
per channel file format, significant improvements in final image quality can be
realized.</p>
<p><b><a name="tiff"></a>TIFF Recording</b></p>
<p>Most cameras offering uncompressed or losslessly compressed recording use TIFF (Tagged Image
File Format) files for that purpose. TIFFs aren't subject to compression
artifacts, but they're very large to gargantuan, depending on the <a href="#resolution">resolution</a>
chosen. The uncompressed TIFFs output by my 2MP camera run 4-14 times larger than the corresponding
JPEGs! Some cameras record <i>compressed TIFFs</i>, which achieve at most a 2:1
to 3:1 reduction in file size using the lossless LZW compression scheme.
Unfortunately, compressed TIFFs aren't as standardized as their uncompressed
counterparts and may not be recognized as TIFFs, even by software claiming to
support compressed TIFFs.</p>
<p>Think of an uncompressed TIFF as the image the camera had right before JPEG compression would
have been applied. Color interpolation from the Bayer
pattern sensor data has already been performed in-camera. The image has already
been requantized to 8 bits per primary color channel. Any <a href="#wb">white balance</a>
settings in effect at exposure time have already been applied.&nbsp;And if <a href="#sharpening">in-camera
sharpening</a> is enabled, the image will have been sharpened as well.&nbsp;</p>
<p><b>JPEG, TIFF or RAW?</b></p>
<p>The best way to determine the recording format best for you is
to <a href="#testing">test</a>  against your own most stringent credible end-uses. If you can live with
<a href="#jpeg">JPEG</a> recording�and most users can�your digital photography will be greatly simplified
on many fronts. Someday cameras may offer losslessly compressed recording in PNG
(Portable Network Graphics) format. Until then, <a href="#tiff">TIFF</a> and <a href="#raw">RAW</a>
remain the formats of choice for applications requiring lossless recording.</p>
<h4><b><a name="compression_choices"></a>Dialing In JPEG Compression Levels</b></h4>

<p>Don't assume that the image quality gained with less compressed recording automatically justifies the potentially huge memory hit
involved on a routine basis.
Many
C-20x0Z users, myself included, find the
moderately compressed 1600x1200 HQ recording mode perfectly acceptable
for all but the most demanding applications�even for 8x10 prints.</p>

<p>As <a href="c-2000z/flash/index.htm#important">dangerous</a> as that strategy
may be, I generally
reserve my least compressed (SHQ) JPEG option for selected
shots. Uncompressed (SHQ TIFF) recording
has its uses�for example, in <a href="c-2000z/low-light/index.htm#dark_field"> dark field subtraction</a> work�but
for me, TIFFs take up way too much memory card space for routine work.&nbsp; A
professional working
in a studio with a stack of large memory cards and the means to unload them
quickly into a nearby computer might feel differently, of course, but that's not
my MO.</p>

<hr>
<h3><b><a name="sharpening"></a>In-Camera Image Sharpening</b></h3>
<p>Before leaving the realm of irreversible pre-exposure decisions, be aware that many experienced digital photographers
<i> strongly</i> recommend against in-camera image sharpening�at least for shots you'll likely
be post-processing. Everyone agrees that sharpening is best saved for the very
last step in any post-processing sequence, so why apply it up front in-camera?</p>
<p>That said, the sharpening algorithm in my C-2020Z hasn't been an obvious
debit with regard to either post-processing or image quality in most instances. I
nevertheless disable in-camera sharpening on a routine basis because I don't
have a good track record when it comes to <a href="c-2000z/flash/index.htm#important">picking
important shots ahead of time</a>. If disabling sharpening has shortened my <a href="#latency">shot-to-shot
latency</a>, I haven't noticed it.</p>

<p>On the C-2020Z, you disable in-camera sharpening by selecting the
&quot;soft&quot; setting in the sharpening menu. The &quot;normal&quot; setting
turns sharpening on. The C-3030Z added a &quot;hard&quot; option with extra
sharpening. The terminology is unfortunate, but at least the control is
there.</p>

<p>You'll find more on <a href="processing.htm#sharpening2">sharpening in
post-processing</a> elsewhere on this site.</p>

<hr>

<h3><a name="wb"></a>White Balance</h3>
<p>Even the most common &quot;white&quot; light sources�the sun, indoor
lighting and flash�differ substantially in color composition. These differences are
well demonstrated in this <a href="http://micro.magnet.fsu.edu/primer/lightandcolor/sources.html">Light
and Color tutorial</a>. Here at the
Earth's surface, for instance, the quality of <a href="#sunlight">sunlight</a>
varies tremendously with the weather and the time of day: Outdoor ambient light
is bluer under overcast skies than it is on clear, sunny days and much redder in
the early morning and late afternoon than around noon. Artificial light is even
more variable. Incandescent light is quite red, while flash is rather blue.
Fluorescent lights generally tend
toward the green but vary significantly with the type of lamp � daylight, cool
white, neutral white, etc. In fact, the fluorescent color casts are problematic
enough to warrant several fluorescent WB presets in my C-5050Z, as shown in the <a href="#wb_table">table
below</a>.</p>
<p>When viewing a scene directly with our own eyes, we tend consider any light
with roughly equal primary color intensities as &quot;white&quot; or at least
neutral, and we
unconsciously correct for subtle biases in the balance of primaries based on
expectations accumulated over a lifetime of visual experience. But cameras
aren't that smart. The light coming off a scene inevitably carries the color bias of the
source. You'll probably be unaware of it at the time, but without help, any camera will faithfully record that bias,
and welcome or not, you'll be seeing it in your photographs. (Why the <a href="vision.htm#brain-eye"> brain-eye</a>
readily applies all manner of corrections to our visions of live scenes but not
to photographs of them, no one knows, but that's the harsh reality photographers
face.)&nbsp;</p>
<p> Since any source-related color bias will be most conspicuous in objects that <i>should
have been white</i> by human standards, photographers have come to think of this
issue as one of <i>white balance</i>, but the real issue is not so much a matter
of whiteness as of neutrality.</p>
<div align="left">
  <table border="0">
    <tr>
      <td valign="top" align="left">When I took the photo at right under
        incandescent light, I was completely oblivious to the now obvious
        reddish cast of my source. Had I taken it using my camera's tungsten white balance
        setting, the cast would have been largely if not completely eliminated.</td>
      <td valign="top" align="left"><a href="c-2000z/lenses/ac2kacc10m.jpg"><img src="c-2000z/lenses/ac2kacc10s.jpg"
        alt="Oly C-2000Z with mounted CLA-1 conversion lens adapter awaiting 43-55 mm step-up ring and B-300 1.7X telephoto converter. Click to see 640x480 version. [D-340L]"
        align="right" border="0" hspace="0" width="160" height="120"></a></td>
    </tr>
  </table>
</div>
<h4>White Balance Controls</h4>
<p> Film photographers intent on WB control
typically have to contend with time-consuming and potentially costly film and/or
filter changes, and their options and wiggle room tend to be rather limited.
Luckily, digital cameras have largely done away with all that. With digital <a href="#wb_settings">white balance (WB)
controls</a>,&nbsp;compensating for unwanted source-related color biases
at recording time can be as quick and easy as navigating a menu. In fact, fingertip WB control is
one the truly great
conveniences in digital photography. In-camera WB adjustments are made by the firmware when the raw CCD
data undergoes color interpolation. If you use <a href="#raw">RAW recording</a>, you'll have to
do your own white balancing in post-processing; otherwise,
the camera will do it for you, with or without your help.</p>
<h4>Gee, It Looked White to Me</h4>
<p>The highly effective auto-WB feature built into your own <a href="vision.htm#brain-eye"> brain-eye system</a>
makes it difficult to appreciate the camera's WB struggle. When you behold clean
snow or any other surface that your brain expects to be pure white, white is
what you see, at least at first glance, regardless of the light source.</p>
<p>But cameras record the light they see without making
judgements about how things <i>should</i> look. Without some intervention, snow in late afternoon sun photographs with a distinct reddish cast. At
times, that may be just the look you're after, but more often than not, pure
white is the goal for snow because that's what anyone standing there would have
seen. And that's where you and the camera's <a href="#wb_settings">WB
settings</a> come in.</p>
<h5>Note: <i>Exposing</i> snow and other bright surfaces correctly is an
entirely different matter, as discussed <a href="#snow">below</a>.</h5>
<h4><a name="wb_settings"></a>WB Settings</h4>
<p>The <b> automatic</b> TTL WB systems found in most current digital cameras work
amazingly well � well enough in fact to be the default setting for most
users � but they're not infallible. Fortunately, many higher-end cameras also
offer manual WB settings allowing you to inform the camera about the dominant illumination at hand in tricky situations likely to trip up auto-WB.&nbsp;</p>
<p>One such situation arises in <a href="c-2000z/flash/index.htm#white">external
flash</a> (EF) work with the internal flash turned off (EF-IF for short).
Disabling the internal flash defeats auto WB in low-light
conditions, at least with my C-2020Z. Manual WB (sunny or overcast) is the only <i>sure</i>
way to keep EF-IF shots from coming out too blue.</p>
<h5>Note: If you know of any other conditions likely
to make auto-WB fail, please drop me an e-line at <a href="mailto:dpFWIW@cliffshade.com">dpFWIW@cliffshade.com</a>.</h5>
<p>WB implementations rapidly have become more and more sophisticated. My
1999-vintage C-2020Z, a star in its time, offered fully automatic TTL WB plus 4 manual WB pre-sets covering
the most commonly encountered lighting situations. By late-2002, my C-5050Z had
auto WB plus 9 presets plus 4 storable custom WB settings and a <a href="#show_me">manual
WB</a> mode, as shown in the table below; even its factory presets are
adjustable.</p>
<table border="2" height="584" width="886">
  <tr>
    <td valign="top" align="left" height="14" width="856" colspan="4">
      <h3><a name="wb_table"></a>Oly C-5050Z White Balance Settings&nbsp;</h3>
    </td>
  </tr>
  <tr>
    <td valign="top" align="left" height="24" width="149"><b>Type</b></td>
    <td valign="top" align="left" height="24" width="331"><b>Setting</b></td>
    <td valign="top" align="left" height="24" width="92"><b>C-2020Z&nbsp;</b></td>
    <td valign="top" align="left" height="24" width="284"><b>Illumination Bias to Correct&nbsp;</b></td>
  </tr>
  <tr>
    <td valign="top" align="left" height="22" width="149">
      Auto</td>
    <td valign="top" align="left" height="22" width="331">
      Auto</td>
    <td valign="top" align="left" height="22" width="92">
      Yes</td>
    <td valign="top" align="left" height="22" width="284">
      Any deviation from neutral</td>
  </tr>
  <tr>
    <td valign="top" align="left" height="96" rowspan="4" width="149">
      <a href="#sunlight">Natural source</a></td>
    <td valign="top" align="left" height="24" width="331">
      <p><a href="#sunny2">Sunny</a></td>
    <td valign="top" align="left" height="24" width="92">
      Yes</td>
    <td valign="top" align="left" height="24" width="284">
      <p>Baseline</td>
  </tr>
  <tr>
    <td valign="top" align="left" height="24" width="331">
      <p><a href="#overcast">Overcast</a></td>
    <td valign="top" align="left" height="24" width="92">
      Yes</td>
    <td valign="top" align="left" height="24" width="284">
      <p>Too blue</td>
  </tr>
  <tr>
    <td valign="top" align="left" height="24" width="331">
      <a href="#evening">Evening (or morning) sun</a></td>
    <td valign="top" align="left" height="24" width="92">
      No</td>
    <td valign="top" align="left" height="24" width="284">
      Too red</td>
  </tr>
  <tr>
    <td valign="top" align="left" height="24" width="331">
      <a href="#shade">Shade</a></td>
    <td valign="top" align="left" height="24" width="92">
      No</td>
    <td valign="top" align="left" height="24" width="284">
      Usually too blue</td>
  </tr>
  <tr>
    <td valign="top" align="left" height="140" rowspan="6" width="149">
      Artificial source&nbsp;</td>
    <td valign="top" align="left" height="20" width="331">
      <p>Tungsten (incandescent, 3,000�K)&nbsp;&nbsp;&nbsp;</td>
    <td valign="top" align="left" height="20" width="92">
      Yes</td>
    <td valign="top" align="left" height="20" width="284">
      <p>Too red</td>
  </tr>
  <tr>
    <td valign="top" align="left" height="24" width="331">Fluorescent, generic*</td>
    <td valign="top" align="left" height="24" width="92">Yes*</td>
    <td valign="top" align="left" height="24" width="284">Too green in general</td>
  </tr>
  <tr>
    <td valign="top" align="left" height="24" width="331">Fluorescent, daylight
      (6,700�K)&nbsp;</td>
    <td valign="top" align="left" height="24" width="92">No</td>
    <td valign="top" align="left" height="24" width="284"></td>
  </tr>
  <tr>
    <td valign="top" align="left" height="24" width="331">Fluorescent, neutral
      white (5,000�K)&nbsp;</td>
    <td valign="top" align="left" height="24" width="92">No</td>
    <td valign="top" align="left" height="24" width="284"></td>
  </tr>
  <tr>
    <td valign="top" align="left" height="24" width="331">Fluorescent, cool
      white (4,200�K)&nbsp;</td>
    <td valign="top" align="left" height="24" width="92">No</td>
    <td valign="top" align="left" height="24" width="284"></td>
  </tr>
  <tr>
    <td valign="top" align="left" height="24" width="331">Fluorescent, white
      (3,200�K)&nbsp;</td>
    <td valign="top" align="left" height="24" width="92">No</td>
    <td valign="top" align="left" height="24" width="284"></td>
  </tr>
  <tr>
    <td valign="top" align="left" height="96" rowspan="4" width="149">Custom
      settings&nbsp;</td>
    <td valign="top" align="left" height="24" width="331">Custom 1</td>
    <td valign="top" align="left" height="24" width="92">No</td>
    <td valign="top" align="left" height="24" width="284"></td>
  </tr>
  <tr>
    <td valign="top" align="left" height="24" width="331">Custom 2</td>
    <td valign="top" align="left" height="24" width="92">No</td>
    <td valign="top" align="left" height="24" width="284"></td>
  </tr>
  <tr>
    <td valign="top" align="left" height="24" width="331">Custom 3</td>
    <td valign="top" align="left" height="24" width="92">No</td>
    <td valign="top" align="left" height="24" width="284"></td>
  </tr>
  <tr>
    <td valign="top" align="left" height="24" width="331">Custom 4</td>
    <td valign="top" align="left" height="24" width="92">No</td>
    <td valign="top" align="left" height="24" width="284"></td>
  </tr>
  <tr>
    <td valign="top" align="left" height="24" width="149"><a href="#show_me">Manual</a></td>
    <td valign="top" align="left" height="24" width="331">Manual, or
      &quot;one-touch&quot;</td>
    <td valign="top" align="left" height="24" width="92">No</td>
    <td valign="top" align="left" height="24" width="284">Any deviation from
      neutral</td>
  </tr>
</table>
<h5>* Table Note: The C-5050Z has no generic fluroescent setting. It's much
better than the C-2020Z at correcting fluorescent color casts, but it forces you
to learn much more than you ever wanted to know about fluorescent lamps.&nbsp;</h5>
<p>Note that the named pre-sets all refer to the <i>source</i> of illumination in
the scene, with no mention of the scene elements reflecting the light to the
camera. That's your cue to select WB pre-sets based on the light source, not on
the subject matter. (Don't get locked into the pre-set names, however � the tungsten
preset might
be profitably applied to any overly red light source.) Now think of the expense
and carrying capacity that would tied up in a collection of optical filters
capable of neutralizing all the sources listed in the <a href="#wb_table">table
above</a>.</p>
<h4><a name="show_me"></a>Manual WB � Show Me Something Neutral, And More</h4>
<p>Newer digital cameras like my Oly C-5050Z offer highly accurate
&quot;one-touch&quot; WB-by-example features that tap your brain power for the white
or neutral recognition piece of the WB equation. A white or gray card carried in your camera bag
provides the neutral standard under this &quot;show me something neutral&quot;
WB scheme. Since &quot;white&quot; papers actually vary substantially in color,
photographic <a href="#gray_card">gray cards</a> are safer for this purpose
because they're guaranteed to be neutral.&nbsp;</p>
<p>Manual WB has other valuable uses. You can warm a shot by
showing your manual WB something blue, or cool the scene by showing it something
red beforehand.&nbsp;Many <a href="ir.htm">digital infrared (IR)</a> enthusiasts
use manual WB to manage the sometimes garish <a href="ir.htm#false_colors">false
color schemes</a> their cameras would otherwise assign to IR images captured
under color recording. (Remember, the concepts of &quot;color&quot; and
&quot;neutral&quot; are completely undefined outside the visible spectrum.)</p>
<h4>WB Fallbacks</h4>
<p>Digital cameras also provide some valuable fallbacks on the WB front:</p>
<ul>
  <li>
    <p style="margin-bottom: 9">You can always check your results on the LCD at
    the scene. You may not pick up subtle WB problems, but it's better than
    nothing.</li>
  <li>
    <p style="margin-bottom: 9">When in doubt, you can bracket for WB, time and
    memory permitting.</li>
  <li>You can usually fix WB problems in post-processing�especially when the
    scene contains something that really <i>is</i> white. Many photo editors
    offer very simple &quot;show me something white&quot; correction schemes.</li>
</ul>
<p>Getting WB right has never been easier.</p>
<h4><a name="sunlight"></a>Sunlight Variations</h4>
<p>Most of the variations observed in the color of sunlight at the Earth's
surface stem from spectral variations in <a href="polarizer.htm#scatter">atmospheric
scattering</a>. In clear air, short (UV-A and blue) wavelengths&nbsp; suffer up to 16 times more
scattering than longer (red and <a href="ir.htm#sources">near IR</a>)
wavelengths because scattering
efficiency by air molecules (N<sub>2</sub>, O<sub>2</sub>, CO<sub>2</sub>, etc.)
varies inversely with the fourth power of wavelength.</p>
<p><a name="sunny2"></a>Direct sunlight here on Earth is yellower (redder and greener) than the light
leaving the sun because the atmosphere scatters a good bit of the blue away
before the light ever reaches you and your subject. (Yes, some of the scattered
blue will eventually scatter back to the surface, but there's still a net loss
of blue.)</p>
<p><a name="overcast"></a>Overcast light is bluer than direct sunlight because visible wavelengths are
all scattered equally well by particles the size of condensed water droplets in
clouds�hence clouds in shades of gray at midday. Scattered blue light falling onto
the cloud tops from above gets tossed back in the mix, now with an even chance
of getting to the ground. There's still a net loss of blue, but under overcast
skies, it's smaller relative to losses at other wavelengths.</p>
<p><a name="shade"></a>Outdoors, shaded areas are illuminated predominantly by
skylight, which is quite blue on sunny days and closer to neutral on overcast
days. Shaded spots under leafy trees can also pick up extra green light
reflected from or transmitted through overhead leaves.</p>
<p><a name="evening"></a>In the morning and evening, sunlight takes a much longer path through the
atmosphere, losing even more blue and some green to scattering along the way.
That's why early and late day sun is redder, and why sunrises and sunsets
feature the warm longwave (red, orange and yellow) colors we so admire.</p>
<p><a href="ir.htm">Near IR</a> wavelengths suffer very little scattering, even
under hazy conditions�hence the incomparable clarity of IR photos. Aerial
surveillance photos are commonly made with <a href="ir.htm#ir_filters">near IR pass filters</a> to take advantage of
this fact.</p>
<hr>

<h3><b><a name="testing"></a>Testing Recording Mode Choices</b></h3>

<p>Only you can decide how best to play the <a href="#jpeg_artifacts"> JPEG artifact</a> vs. file size
trade-off and the in-camera <a href="#raw">color interpolation</a> and <a href="#sharpening">sharpening</a> 
games.
The proper balances depend critically on your equipment and quality needs.
Fortunately, digital cameras make the required testing a snap.</p>

<p>A simple but useful <b>recording mode test</b> requires 2 sample scenes�one in
bright sunlight, preferably with large areas of low contrast, and the other in
open shade with richly detailed shadows. Shooting from a tripod using a remote
if available, capture each scene with identical exposure settings across the
recording modes to be compared. Print the images at<i> constant final
subject size</i> to see what's acceptable to you. Pay close attention to</p>

<ul>
  <li>Overall sharpness and lack of pixellation at realistic print viewing distances.</li>
  <li>Areas where colors merge�<a href="#jpeg_artifacts">JPEG artifacts</a> will be most apparent here.</li>
</ul>
<p>Let the most demanding credible end-uses for your images be your guides.</p>

<div align="left">
  <table border="0" cellspacing="0" cellpadding="0">
    <tr>
      <td valign="bottom"><a href="index.htm#site_index"><img border="0" src="art_index.gif" width="133" height="34"></a></td>
      <td valign="bottom"><a href="#page_index"><img border="0" src="up.gif" width="41" height="51"></a></td>
      <td valign="bottom"><a href="filters.htm"><img border="0" src="next_art.gif" width="133" height="34"></a></td>
    </tr>
  </table>
</div>

<hr>

<h2><b><a name="resolving"></a>Resolving Power</b></h2>
<p>Determining and describing the optical quality of a camera lens turns out to
be a very complex and highly technical enterprise involving issues of
distortion, aberration (primarily chromatic) and <i>resolving power</i>�the
ability to distinguish small image features (like line pairs) at small
separations. Resolving power depends primarily on&nbsp;</p>
<ul>
  <li>
    <p style="margin-bottom: 9"> the maximum sharpness or <i>resolution</i> of the lens
    (here measured in distinguishable line-pairs per mm), and&nbsp;</li>
  <li>
    <p style="margin-bottom: 9"> the image <i> contrast</i> it delivers at scales at and above maximum resolution.&nbsp;</li>
</ul>
<p> To complicate matters further, these 2 attributes are largely uncoupled�for instance, high marks on sharpness don't
guarantee stellar contrast performance. A top-notch lens needs to perform well
on both fronts, but that'll cost you.</p>
<h5>Technical note:&nbsp; The term &quot;resolution&quot; means different things
when applied to lenses and CCDs. <a href="#resolution">CCD resolution</a> refers
to the sensel count (say, 1600x1200) in the chip's active image-forming area.
For optimum camera performance, lens and CCD resolutions must be carefully
matched.</h5>
<p>The issue of resolving power in digital cameras is further complicated by the
discrete nature of CCD sensels, but resolving power remains a useful concept when
applied to specific lens-CCD combinations. Until digital cameras sporting
interchangeable lenses become commonplace, resolving power will remain a
property of the digital camera as a whole.</p>
<p>Alas, the topic of lens-CCD quality is so complex that widely accepted,
easy-to-interpret measures are unlikely to become readily available to
prospective digital camera buyers, at least in the foreseeable future. Some of
the <a href="index.htm#major">major digital camera review sites</a> have taken
to posting test images based on a bewildering assortment of standard test
patterns, but even the experts seem to have a hard time agreeing on how these should be
interpreted. Some practical gauge of combined camera-lens resolution is sorely
needed.</p>
<p>This morass tremendously complicates the process of selecting a digital
camera for serious photography, but once you've cast your lot, you can rely on
some fairly simple lens-related quality principles to guide your
technique.&nbsp;</p>
<hr>
<h3><b><a name="resolving_basics"></a>Resolving Power Basics</b></h3>
<p><a href="#aperture">Aperture</a> is the key to <a href="#resolving">resolving
power</a> management. Large apertures allow unwanted <a href="#prism">prism
effects</a> to creep in from the edges of the lens,&nbsp; while small openings
promote <a href="#diff_blur">diffraction blurring</a> at the iris. The trick is
to find the aperture corresponding to the <a href="#resolving_sweet">resolving
power sweet spot</a> for your lens and use it whenever
you can.</p>
<h4><a name="prism"></a>Prism effects</h4>
<p>It's an inescapable
fact of lens design and manufacture: All lenses perform better at less than wide-open aperture
because optical quality&nbsp; inevitably falls off toward lens edges. Chromatic aberration (the focusing of
different wavelengths coming from the same subject point onto different points on the
image receiver) is one of the most commonly encountered <i>&quot;prism&quot; or
&quot;edge&quot; or &quot;off-axis&quot;</i> lens effects, especially in less
expensive lenses.</p>
<h4><a name="diff_blur"></a>Diffraction blurring&nbsp;</h4>
<p>Diffraction blurring occurs when incoming light diffracts (bends) around the
edge of the iris instead of passing cleanly through. For a lens of focal length
L, the higher the <a href="#f-number">f-number</a> N, the smaller the physical
aperture (L/N) becomes. The
closer the physical aperture gets to the wavelengths of visible light (400-700
nm), the greater the bending at the
iris and the greater the blurring at the image plane will be.
Thankfully, diffraction blurring isn't as damaging to image quality as
blurring due to poor focusing, but it's clearly noticeable in most digital
cameras at f/8 and smaller apertures. In fact, few digital cameras offer
apertures smaller than f/8 for that very reason.&nbsp;</p>
<p>At any given <a href="#f-number">f-number</a>, digital cameras are more prone to diffraction blurring
than 35 mm cameras. The reason boils down to image receiver size. The 8-10 mm
diagonals typical of consumer-grade digital camera CCDs are small compared to the 43 mm
diagonal of the 35 mm film frame, and small digital diagonals
require lenses with very short focal lengths � typically in the 5-20 mm range. At
a wide-angle zoom setting of 5 mm, a digital f/8 exposure calls for a tiny
physical aperture of 5/8 = 0.625 mm. The same shot with a 35 mm camera would
involve a physical aperture of around 24/8 = 3 mm.&nbsp;</p>
<p>That's why current consumer-grade digital camera lenses are said to be <i>diffraction-limited</i>.
Expect this to change only when physically large CCDs approaching
the size of the 35 mm film frame become affordable, but don't hold your breath.</p>
<hr>
<h3><b><a name="resolving_sweet"></a>Resolving Power Sweet Spot</b></h3>
<p>OK then, how does resolving power bear on exposure strategy?</p>
<p>Practically speaking, resolving power peaks at the aperture(s) striking the
best balance between diffraction blurring and off-axis effects. Like many a 35 mm camera lens,
the f/2.0 lens on my 2.1MP C-20x0Z reaches maximum resolving power at ~2 <a href="#stops">full stops</a> down from wide
open � i.e., around f/4 at wide angle and f/5.6 at full zoom. For the slightly
faster f/1.8 lens on my 5.2MP C-5050Z, informal testing suggests a resolving
power sweet spot around f/2.8 to f/4.</p>
<table border="1">
  <tr>
    <td valign="middle" align="center" colspan="2">
      <h3 align="left">Informal Resolving Power Test For the 5.2MP C-5050Z</h3>
    </td>
  </tr>
  <tr>
    <td valign="middle" align="center"><img border="0" src="images/resolve-18.jpg" width="386" height="231"></td>
    <td valign="middle" align="center"><img border="0" src="images/resolve-20.jpg" width="386" height="237"></td>
  </tr>
  <tr>
    <td valign="middle" align="center">f/1.8 @ 1/1000 sec</td>
    <td valign="middle" align="center">f/2.0 @ 1/1000 sec</td>
  </tr>
  <tr>
    <td valign="middle" align="center"><img border="0" src="images/resolve-28.jpg" width="386" height="238"></td>
    <td valign="middle" align="center"><img border="0" src="images/resolve-40.jpg" width="386" height="238"></td>
  </tr>
  <tr>
    <td valign="middle" align="center">f/2.8 @ 1/800 sec</td>
    <td valign="middle" align="center">f/4.0 @ 1/400</td>
  </tr>
  <tr>
    <td valign="middle" align="center"><img border="0" src="images/resolve-56.jpg" width="386" height="238"></td>
    <td valign="middle" align="center"><img border="0" src="images/resolve-80.jpg" width="386" height="237"></td>
  </tr>
  <tr>
    <td valign="middle" align="center">f/5.6 @ 1/200 sec</td>
    <td valign="middle" align="center">f/8.0 @ 1/100 sec</td>
  </tr>
</table>
<h5><b>Table notes:</b> These handheld 388x238 crops came from otherwise
unedited 2560x1920 SHQ JPEG images taken in landscape program mode at full
wide-angle zoom (FL = 7.1 mm) with <a href="#sharpening">in-camera sharpening</a>
disabled at -5. Differences in detail capture are best appreciated when viewed
at 200-400%. Thanks to Tom Lanckamp for the idea of using chain link fence as a
resolving power test target. Next time, I'll use a tripod and remote control to
eliminate any blurring due to <a href="#shake">camera shake</a>.</h5>
<p> Even at relatively wide f/2.8 to f/4 sweet-spot apertures,
I usually
end up with <a href="#dof">DOF</a> to burn � near that of a 35 mm camera at
f/22! Better yet, the attendant fast shutter speeds are good insurance against <a href="#shake">camera shake,</a> which remains my No.
2 photographic nemesis � right after my woeful lack of creativity. Since
diffraction blurring gets particularly nasty at f/8
and smaller apertures at current CCD sizes, I try not to go there now, but I
sure wish I'd known that when I first went digital.</p>
<div align="left">
  <table border="2" style="font-size: 10pt">
    <tr>
      <td valign="top" align="left"><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;<b>Optimum
        Aperture for Resolving Power</b></td>
    </tr>
    <tr>
      <td valign="top" align="left">
<p>Chances are, the aperture sweet spot for your lens is also ~2 <a href="#stops">full stops</a> down from wide
open. For the sharpest images your camera can muster, target that aperture when
you can and work to avoid f/8 and smaller apertures. If bright ambient light
keeps you away from your aperture sweet spot, consider mounting a <a href="filters.htm#nd"> neutral density (ND)
filter</a> or a <a href="polarizer.htm">polarizer</a>.</p>
      </td>
    </tr>
  </table>
</div>
<p>Not surprisingly, Program mode usually pursues
a very similar strategy in both the C-2020Z and the C-5050Z, but both cameras seems to settle on f/2.8 more often than f/4. (Hmmm, maybe
they know something I don't.)</p>
<hr>
<h3><b>Yes, Digital Lens Quality Matters</b></h3>
<p>Don't fall into the trap of thinking that you can scrimp on a digital camera
with a cheap lens just because the CCD's pixels are a lot coarser than
the silver halide grains in film. Many digital photographers have come to realize
that image quality can
easily become lens-limited, starting somewhere between 1.5 and 2.1 megapixels
(MP). Lens quality clear counts at 3.3MP and above.</p>
<p>The designers behind the emerging crop of 2MP cameras with very long, very
sharp electronically stabilized zoom lenses like the new Oly C-2100UZ and
the Sony Cybershot DSC-F505 may well be zeroing in on a sweet spot where field
flexibility, image sharpness, low-light performance and file size all come together quite
nicely. These new-generation 2MP cameras promise to give 3MP offerings with
lesser lenses a run for their money.</p>

<div align="left">
  <table border="0" cellspacing="0" cellpadding="0">
    <tr>
      <td valign="bottom"><a href="index.htm#site_index"><img border="0" src="art_index.gif" width="133" height="34"></a></td>
      <td valign="bottom"><a href="#page_index"><img border="0" src="up.gif" width="41" height="51"></a></td>
      <td valign="bottom"><a href="filters.htm"><img border="0" src="next_art.gif" width="133" height="34"></a></td>
    </tr>
  </table>
</div>

<hr>

<h2><b><a name="dof"></a>Depth of Field (DOF)</b></h2>

<p>Technically, focus is perfect only in a single plane, which presumably
coincides with some part of the subject.
In practice, however, focus appears <i> acceptably sharp</i> to the <a href="vision.htm#brain-eye">brain-eye
system</a> for some
distance in front of and behind the plane of true focus. This range of acceptable focus is
called <i>depth of field (DOF).</i> Relative to the camera, the nearest plane of
acceptable focus is called the <i>near limit of DOF</i> and the farthest plane,
the <i>far limit</i>. These boundaries are seldom equidistant from the plane of
true focus. In <a href="#hyperfocal">hyperfocal technique</a>, for instance, the
near limit may be at 3 feet, the plane of true focus at 6 feet, and the far
limit at infinity.</p>

<p>It's important to distinguish DOF from the locations of its near and far
limits. DOF is the distance <i>between</i> the near and far limits. An important
rule of thumb pertaining to non-close-up work states that if the subject
occupies a constant portion of the frame, DOF will also remain constant, even
though the near and far limits shift substantially as one goes from a close-in
wide-angle shot to a telephoto shot from afar.</p>

<p>DOF is further complicated by the fact that DOF and its near and far limits
all vary somewhat independently with <a href="#dof_aperture">aperture</a>,
<a href="#magnification">
magnification</a>, <a href="#dof_focal_length"> focal length</a> and, of course, with
the definition of &quot;acceptable focus&quot;. The last is usually
specified as the diameter of the largest acceptable <a href="#confusion">circle of
confusion</a>, which can be thought of as the image of an imperfectly focused
point image projected onto the true focal plane.&nbsp;</p>

<h4>Working with DOF</h4>

<p>Achieving a DOF encompassing just the elements that need to be in focus is
always an important goal in photography, digital and film alike. To match what the eye sees, landscapes generally require a very large
DOF including both near and distant scene elements. In
this arena, digital cameras deliver DOF film photographers can only dream of. In
close-ups, even digital cameras struggle to provide the DOF to cover a single flower, let
alone the background, but film cameras struggle much more. In portraiture, however,
the worm turns. DOF is often
purposely reduced to help separate in-focus subjects from their less important
blurred backgrounds. For film photographers, <a href="#dof_limiting_scene">limiting
DOF</a> is easy, but digital photographers find it a struggle. These consistent
differences in film vs. digital DOFs flow directly from differences in the sizes
of the image receivers typically involved:&nbsp; Most digital sensors are much
smaller than 35 mm, medium format and large format film frames.</p>

<h4>The Road Ahead</h4>
<p>The remainder of this lengthy and rather complicated section will cover</p>
<ul>
  <li>
    <p style="margin-bottom: 9"><a href="#determinants">Determinants of DOF</a>�
    including <a href="#dof_aperture">aperture</a>, <a href="#magnification">magnification</a>,
    <a href="#dof_focal_length">focal length</a>, a wrap-up <a href="#dof_summary">summary</a>
    and
    several handy <a href="#dof_thumb">rules of thumb</a></li>
  <li>
    <p style="margin-bottom: 9"><a href="#limiting_dof">Limiting DOF</a>�both
    at the <a href="#dof_limiting_scene">scene</a> and in <a href="#dof_limiting_post">post-processing</a>,
    with a glance at <a href="#separation">other means of subject-background separation</a></li>
  <li>
    <p style="margin-bottom: 9"><a href="#mag_rules">Magnification Rules</a>�wherein
    the
    single most important factor determining DOF gets special treatment</li>
  <li>
    <p style="margin-bottom: 9"><a href="#andrzej">Relating Digital to 35 mm
    Camera DOF</a>�leveraging your film experience</li>
  <li><a href="#hyperfocal">Hyperfocal Technique</a>�when pretty much everything needs to
    be in focus</li>
</ul>
<p>We'll tackle these topics one by one in the order listed.</p>
<hr>
<h3><b><a name="determinants"></a>Determinants of DOF</b></h3>
<p> For close-up work (when camera-subject distance is small relative to the <a href="#hyperfocal">hyperfocal
distance</a>), DOF varies directly with <a href="#dof_aperture"> aperture
f-number</a> and even more strongly and inversely with <a href="#magnification">magnification</a>,
which depends in part on focal length. With more distant subjects,
<a href="#dof_focal_length"> focal length</a>
comes directly into play as well.</p>
<p> <a href="#dof_focal_length"> Focal length</a> plays a critical role in DOF
considerations, so we'd better get our signals straight. Often, we'll need the actual focal length (f) of the lens
or zoom setting at hand. For digital cameras, actual focal lengths typically
fall in the 5-20 mm range. When taking advantage of relationships long ago worked
out for 35 mm cameras, however, we'll sometimes need to express focal length as the <i>equivalent
focal length</i> (f<sub>35</sub>, EFL) of a 35 mm camera. Because the 35 mm
frame is 2-5 times larger than most digital camera image receivers (CCDs, CMOS
sensors, etc.), the values of f and f<sub>35</sub>  usually differ substantially
for a given camera. For the 3x zoom lens in my Oly C-5050Z, f (actual focal
length) = 7.1 - 21.3 mm, while f<sub>35</sub>  = EFL = 35 - 105 mm. Using the
wrong version in a formula involving focal length is likely to generate a large
error.&nbsp;</p>
<h4><b><a name="dof_aperture"></a>Aperture</b></h4>
<p>At any camera-subject distance, the narrower the <a href="#aperture">aperture</a>
(the larger the f-number), the greater the DOF. For close-ups, DOF doubles for
every 2 stops of decreased aperture.&nbsp;</p>
<blockquote>
  <p><b><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;Aperture is
  the only DOF determinant that doesn't affect composition.</b></p>
</blockquote>
<p>Unfortunately, opening up the short focal length lens in a digital camera won't
always <a href="#limiting_dof">limit DOF</a> enough to achieve good
subject-background separation via selective focus.&nbsp;</p>
<h4><b><a name="magnification"></a>Magnification</b></h4>
<p> Magnification is the strongest single determinant of DOF,
as discussed further <a href="#mag_rules">below</a>. The greater the magnification, the
less DOF you'll get.</p>
<p> Technically, <i>magnification</i> is defined as</p>
<blockquote>
<p><b>M = image size / subject size = f / (f - S<sub>o</sub>)</b></p>
</blockquote>
<p>where <i>f</i> is the actual focal length (not the 35 mm EFL) and <i>S<sub>o</sub></i>
is the distance from the front principal plane of the lens to the subject.&nbsp;Of
course, f and S<sub>o</sub> must be in the same units.</p>
<p>Practically speaking, it's often simpler to think of magnification in terms
subject size relative to the image frame.</p>
<blockquote>
  <p><b><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;The larger
  the subject appears in the frame, the less DOF there'll be.</b></p>
</blockquote>
<p>How magnification affects DOF depends to some extent on camera-subject
distance S<sub>o</sub>. In close-ups at fixed f-number, DOF varies inversely with M<sup>2</sup>
and is effectively independent of focal length. Thus, halving subject size <i>as seen in the
image</i> quadruples DOF. At longer camera-subject distances, the relationship
between DOF and magnification becomes more complex, but they still vary
inversely.</p>
<p>Regardless of focal length and camera-subject distance, it's always true that</p>
<blockquote>
<p><b><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;DOF remains constant at constant image size and aperture.</b></p>
</blockquote>
<p>Whether you keep your
frame filled with a flower or a mountain, DOF will remain the same whether
you're close in at wide angle or farther away at full zoom.</p>
<h4> <b><a name="dof_focal_length"></a>Focal Length</b></h4>
<p>At constant magnification M and f-number N, a shorter lens will tend to have a
narrower near DOF and a wider far DOF than a longer lens, but total DOF will be
about the same. In close-up work, focal length has little effect on DOF
proper, but when distant picture elements come into play, focal length enters in
two important ways:&nbsp;</p>
<ul>
  <li>
    <p style="margin-bottom: 9">When working with a near subject, the longer the lens, the fuzzier
    out-of-focus background elements become,
    in direct proportion to focal length.</li>
  <li>Conversely, shorter lenses tend to push out the distance to the farthest point
in focus�the far limit of DOF�often all the way to infinity. This phenomenon forms the
    basis for <a href="#hyperfocal">hyperfocal technique</a>.&nbsp;</li>
</ul>
<p>Close-ups aside, at fixed aperture and camera-subject distance,</p>
<blockquote>
  <p><b><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;The longer
  the lens, the less DOF there'll be.</b></p>
</blockquote>
<p>On the digital side, you can generally count on more DOF than you're
likely to need at all but the widest apertures, thanks to the small CCDs and
very short lenses found in most consumer digital cameras. The C-20x0Z's 8 mm diagonal CCD and 6.5-19.5 mm zoom lens
are typical
in this regard.</p>
<h4><a name="dof_summary"></a>Putting It All Together</h4>
<p>At last, the short answer on the factors determining DOF:</p>
<div align="left">
  <table border="2">
    <tr>
      <td colspan="4">
        <h4>DOF Determinants&nbsp;in a Nutshell</h4>
      </td>
    </tr>
    <tr>
      <td><b>Close-up?&nbsp;</b></td>
      <td><b>F-number N&nbsp;</b></td>
      <td><b>Magnification M&nbsp;</b></td>
      <td><b>Focal Length f&nbsp;</b></td>
    </tr>
    <tr>
      <td>Yes</td>
      <td>DOF � N</td>
      <td>DOF � 1 / M<sup>2</sup></td>
      <td>n/a</td>
    </tr>
    <tr>
      <td>No</td>
      <td>DOF ~� N</td>
      <td>DOF ~� 1 / M<sup>2</sup></td>
      <td>Inverse</td>
    </tr>
  </table>
</div>
<p>where &quot;�&quot; means &quot;proportional to&quot; and &quot;~�&quot;
means &quot;roughly proportional to&quot;.</p>
<p>Mathematically, for any lens,&nbsp;</p>
<div align="left">
  <blockquote>
  <table border="0">
    <tr>
      <td valign="top" align="left" width="49"><b>DOFL</b></td>
      <td valign="top" align="left" width="708"><b>= c * N * (1+M / p) / (M<sup>2</sup>
        * (1 � (N * c) / (f * M))</b></td>
    </tr>
    <tr>
      <td valign="top" align="left" width="49"></td>
      <td valign="top" align="left" width="708"><b>= c * N<sub>e</sub> / (M<sup>2</sup>
        * (1 � (S<sub>o</sub> - f) / h<sub>1</sub>))</b></td>
    </tr>
    <tr>
      <td valign="top" align="left" width="49"></td>
      <td valign="top" align="left" width="708"><b>~ c * N<sub>e</sub> / M<sup>2</sup>
        for close-ups with S<sub>o</sub> - f � h<sub>1</sub>&nbsp;</b></td>
    </tr>
  </table>
  </blockquote>
</div>
<p>where</p>
<ul>
  <li>DOFL is the near or far <i>limit</i> of depth of field</li>
  <li>c = largest acceptable <a href="#dof_circle"> circle of confusion</a></li>
  <li>f = actual focal length = (S<sub>o</sub>  * M) / (1 + M)</li>
  <li>d = physical aperture diameter</li>
  <li>N = aperture f-number = d / f</li>
  <li>S<sub>o</sub> = camera-subject distance = distance from the camera to the plane of true
    focus</li>
  <li>M = <a href="#magnification"> magnification</a> = f / (S<sub>o</sub> - f)&nbsp;</li>
  <li>
    <p style="margin-bottom: 9">p = pupil magnification (1 for all but wide-angle lenses, for which p &gt;
    1)</li>
  <li>N<sub>e</sub> = effective f-number = N * (1 + M / p)</li>
  <li>h<sub>1</sub>= f<sup>2 </sup>/ (N * c) = <a href="#hyperfocal"> hyperfocal distance</a> for unitary p&nbsp;</li>
</ul>
<p>To calculate DOFL<sub>near</sub>, use the &quot;+&quot; in &quot;�&quot; in the
equations above; the &quot;-&quot; gives DOFL<sub>far</sub>. A zero or negative
denominator means that DOFL<sub>far</sub> has become infinite. Of course, all lengths
must use the same unit, typically millimeters.</p>
<p>A particularly useful reformulation of the DOF limit equations emphasizing
the influences of focusing distance S<sub>o </sub>and focal length f,</p>
<p class="MsoNormal" style="MARGIN-LEFT: 0.5in"><b>DOFL<sub>far</sub> = S<sub>o </sub> /
[h<sub>1 </sub>/ (S<sub>o</sub>  - f) - 1]</b></p>
<p class="MsoNormal" style="MARGIN-LEFT: 0.5in"><b>DOFL<sub>near</sub> = S<sub>o
</sub> / [h<sub>1 </sub>/ (S<sub>o </sub> - f) + 1]</b></p>
<p>assumes that h<sub>1</sub> is known, perhaps from a table or from a previous
special-case calculation like the one behind <a href="#hyperfocal_simple">A
Simplified Hyperfocal Technique</a> below.&nbsp;</p>
<h4><a name="dof_thumb"></a>Digital DOF Rules of Thumb</h4>
<p>The DOF limit (DOFL) equations above can be mined for practical DOF insights applicable to all
cameras:</p>
<ul>
  <li>
    <p style="margin-bottom: 9">At any f and S<sub>o</sub>, DOFL<sub>far</sub> grows faster than
    DOFL<sub>near</sub> as S<sub>o</sub>  increases.</li>
  <li>
    <p style="margin-bottom: 9"> In <i>close-ups</i>,<i> </i>DOF (the distance
    between the near and far limits) doubles for
every 2 stops of decreased aperture (increased f-number).</li>
  <li>A shorter lens will always have a
narrower near DOF (S<sub>o</sub> - DOFL<sub>near</sub>) and a wider far DOF (DOFL<sub>near</sub>
    - S<sub>o</sub>) than a longer lens, but DOF (the distance between the near
    and far limits) will stay
about the same at constant magnification M and f-number N.</li>
</ul>
<p>Since S<sub>o</sub> � f almost always holds for digital cameras based on
small CCDs and CMOS sensors, the DOF limit equations simplify to&nbsp;</p>
<p class="MsoNormal" style="MARGIN-LEFT: 0.5in"><b>DOFL<sub>far</sub> = S<sub>o</sub><sup>2</sup><sub>
</sub>/ (h<sub>1 </sub>- S<sub>o</sub>)</b></p>
<p class="MsoNormal" style="MARGIN-LEFT: 0.5in"><b>DOFL<sub>near</sub> = S<sub>o</sub><sup>2</sup><sub>
</sub>/ (h<sub>1 </sub>+ S<sub>o</sub>)</b></p>
<p>at which point some very useful <b> digital DOF rules of thumb</b> come into
view:&nbsp;</p>
<ul>
  <li>
    <p style="margin-bottom: 9"> At S<sub>o</sub> = h<sub>1</sub> / n, where n
    is any positive number, DOFL<sub>near</sub> = h<sub>1</sub> / (n + 1) and
    DOFL<sub>far</sub> = h<sub>1</sub> / (n - 1).</li>
  <li>
    <p style="margin-bottom: 9">Whenever S<sub>o</sub> reaches or exceeds h<sub>1</sub>,
    DOFL<sub>far</sub> goes to infinity.</li>
  <li>
    <p style="margin-bottom: 9"> At S<sub>o</sub> = h<sub>1</sub>, DOFL<sub>near</sub>
    = h<sub>1</sub> / 2. (This important special case forms the basis for common
    <a href="#hyperfocal">hyperfocal technique</a>.)</li>
  <li>
    <p style="margin-bottom: 9"> At S<sub>o</sub> = h<sub>1</sub> / 3, the DOFL<sub>far</sub>
    is
    exactly twice the near.</li>
  <li>At S<sub>o</sub> � h<sub>1</sub>, DOFL<sub>near</sub> and DOFL<sub>far</sub>
    both converge on c * N<sub>e</sub> / M<sup>2</sup>, which is why DOF shrinks
    to mere millimeters in macro work.&nbsp;</li>
</ul>
<p>Note, however, that all these relationships become far more complicated in
close-ups where S<sub>o</sub> � f no longer holds.</p>
<h5>Acknowledgements: Much of this section is adapted from <a href="http://www.photo.net/photo/optics/lensTutorial.html">David
Jacobsen's photo.net Lens Tutorial</a>. Thanks also to Anatoli ?? for finding
some initial errors in the discussion above, and for recommending an emphasis on
the DOF reformulations based only on distances.</h5>
<hr>
<h3><b><a name="limiting_dof"></a>Limiting DOF</b></h3>
<p>Film photographers working with 35 mm SLRs often go to great lengths to
extend DOF, but in digital work, the real challenge often comes in limiting DOF to
achieve <i>selective focus</i>�e.g., to separate the subject from the background in a
portrait by blurring the background.</p>
<p>For an interesting discussion of the power of selective focus, see Tony
Spadaro's <a href="http://www.homeusers.prestel.co.uk/magor/tony/sharp%20enough.htm">Sharp
Enough for You?</a> essay.</p>
<h4><a name="dof_limiting_scene"></a>At the Scene</h4>
<p>To separate subject and background by blurring the latter in-camera, apply these measures alone or in
combination:</p>
<div align="left">
  <table border="2">
    <tr>
      <td valign="top" align="left" colspan="2">
        <h4>Blurring the Background</h4>
      </td>
    </tr>
    <tr>
      <td valign="top" align="left"><b>Find a soft background</b></td>
      <td valign="top" align="left">Look around for textured surfaces, fuzzy
        edges and even motion to soften the background naturally. Fabrics draped
        in gentle folds back up many a portrait, but Aspen leaves
        quaking in the breeze can have the same effect.</td>
    </tr>
    <tr>
      <td valign="top" align="left"><b>Distance the subject from the background
        *</b></td>
      <td valign="top" align="left">Arrange your shot to maximize the physical
        separation between subject and background. All other things being equal,
        the farther apart subject and background are, the less sharply focused the
        background will be.</td>
    </tr>
    <tr>
      <td valign="top" align="left"><b>Focus in front of the subject *</b></td>
      <td valign="top" align="left">If your manual focus is up to the challenge,
        pushing the subject closer to your far limit of DOF will hopefully push
        the background beyond it.</td>
    </tr>
    <tr>
      <td valign="top" align="left"><b>Back off and zoom in *</b></td>
      <td valign="top" align="left">Frame your shot with the maximum possible magnification (subject
    size) consistent with your photographic intent. Then move away from the
        subject and zoom back in to get the framing you need. Remember, DOF varies inversely with the <i>square</i>
    of magnification.</td>
    </tr>
    <tr>
      <td valign="top" align="left"><b>Open up</b></td>
      <td valign="top" align="left">Use the largest possible aperture in aperture-priority or manual mode. If bright
    lighting gets in the way, consider mounting a <a href="filters.htm#nd"> neutral density (ND)
filter</a> or shading your subject. Note
that most <a href="filters.htm#polarizers">polarizers</a>  make handy 2-stop ND
filters in the absence of polarized light.</td>
    </tr>
  </table>
</div>
<p>* These tricks take advantage of the fact that&nbsp;</p>
<blockquote>
  <p><b><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;At constant
  magnification, the blurring of distant background points is proportional to
  focal length.</b></p>
</blockquote>
<p style="margin-bottom: 9">If you can't back off, try using
    macro focusing if you're close enough to your subject.
<h4><a name="dof_limiting_post"></a>Post-Processing for Selective Focus</h4>
<p>Note that some digital photographers prefer to ignore DOF at the scene and blur the background in
post-processing. Jeff Drabble of New Zealand described his method on <a href="index.htm#rpd">RPD</a>:</p>
<blockquote>
<h5>Cut your subject and paste to a new layer. Add as much blur as you want to
the background layer, including the subject if you like - it doesn't matter -
and now, if your subject is on the top layer, the job is done.&nbsp;</h5>
<h5>If you do it all on one layer, you are constrained by the accuracy of your
original selection, and you are also likely to end up with the hard, unnatural
edge that others here have mentioned. If you use a layer, it means that a little
error will only reveal the same part of the picture beneath, albeit blurred if
you have carried out this step. Working with layers gives you the opportunity to
feather parts of the picture together, giving a more natural, flowing look.</h5>
  <h5>It is often easier to do a rough cut-out of the subject and then, with it
  on the top layer, use a feather-edged eraser to remove the remaining, unwanted
  background areas. This helps alleviate the unnatural, hard-edged cutout.</h5>
  <h5>If you want to graduate the blur to simulate a gradual roll-out of the
  depth of field, you can take sections of the background, layer them, apply
  differing levels of blur and feather their edges to blend them.</h5>
</blockquote>
<p> I have yet to try background blurring in post-processing, but I hear that
it's not for the beginner. Some claim that they can easily spot &quot;fake&quot;
blurred backgrounds, but others like Jeff find the effect very realistic with
the appropriate effort and technique.</p>
<h4><a name="separation"></a>Other Means of Separation</h4>
<p><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;Keep in mind
that selective focus via limited DOF is but one of many ways to achieve <i>subject/background
separation</i>. Other potential degrees of separation include</p>
<ul>
  <li>
    <p style="margin-bottom: 9">lighting</li>
  <li>
    <p style="margin-bottom: 9">composition</li>
  <li>
    <p style="margin-bottom: 9">color</li>
  <li><a href="#perspective">perspective</a></li>
</ul>
<p>These separation approaches can be just as effective as selective focus but
tend to be even less straightforward in their application.</p>
<hr>
<h3><b><a name="mag_rules"></a>Magnification Rules</b></h3>
<p><a href="#magnification">Magnification</a> is at once the most important
determinant of DOF and the easiest to overlook in practice. Since it plays
heavily into composition via both subject size and perspective, it merits a
little individual attention here.</p>
<h4><a name="dof_mag"></a>DOF and Magnification</h4>
<p>Try to keep these important magnification and camera-subject distance
relationships in mind:</p>
<ul>
  <li>
    <p style="margin-bottom: 9">The more magnified the subject�the more frame
    it fills�the less DOF you'll have, regardless of the focal length used to
    achieve that magnification.</li>
  <li>Conversely, at constant subject size, DOF will remain constant whether
you're shooting close in at wide angle or with a long lens from afar.</li>
</ul>
<h4><a name="perspective"></a>Perspective</h4>
<p>Let's pause for a moment to examine the surprisingly complex trade-offs
encountered in the camera-subject distance versus zoom decision.</p>
<p>Bear in mind that perspective changes dramatically as you move in and out,
even if you zoom to maintain subject size relative to the frame. At constant
aperture and subject size, DOF won't change, but the&nbsp;closer in you are, the
shorter the focal length required, the wider the resulting angle of view and the
smaller&nbsp;background elements&nbsp;will appear relative to the subject. The
greater sense of depth imparted by the close-in, wide angle perspective may well
offset at least some of the <a href="#separation"> subject/background separation</a> lost to excessive
DOF on the digital side.</p>
<p>Moving away from your subject and zooming back in affords a narrower, more
compressed perspective with greater blurring of out-of-focus background elements.
These effects can also be quite valuable, but the longer the lightpath between
subject and camera, the more your image may suffer from atmospherics�dust,
haze, thermal currents, etc. Also, the longer the focal length, the greater the
risk of <a href="#shake">camera shake</a>, particularly in handheld shots.</p>
<div align="left">
  <table border="1" width="912" height="241">
    <tr>
      <td colspan="3" valign="top" align="left" width="1062" height="21">
        <h4>Change in Perspective With Focal Length and Distance To Subject</h4>
      </td>
    </tr>
    <tr>
      <td valign="top" align="left" width="728" height="61">C-5050Z Lens
        Configuration</td>
      <td valign="top" align="center" width="160" height="61">Native at full
        zoom</td>
      <td valign="top" align="center" width="162" height="61">Native at minimum
        zoom with 0.7x wide-angle converter</td>
    </tr>
    <tr>
      <td valign="top" align="left" width="728" height="21">EFL</td>
      <td valign="top" align="center" width="160" height="21">105 mm</td>
      <td valign="top" align="center" width="162" height="21">25 mm</td>
    </tr>
    <tr>
      <td valign="top" align="left" width="728" height="21">Camera-subject
        distance</td>
      <td valign="top" align="center" width="160" height="21">~10 m</td>
      <td valign="top" align="center" width="162" height="21">~2 m</td>
    </tr>
    <tr>
      <td valign="top" align="left" width="728" height="87">In each lens
        configuration, the black 350Zs filled the viewfinder frame at the scene,
        but the resulting photos have very different perspectives and impacts.</td>
      <td valign="top" align="center" width="160" height="87"><a href="images/coupe-105mm.jpg"><img border="0" src="images/coupe-105mm@.jpg" alt="Perspective at 105 mm [C-5050Z]" width="160" height="100"></a></td>
      <td valign="top" align="center" width="162" height="87"><a href="images/coupe-25mm@.jpg"><img border="0" src="images/coupe-25mm@.jpg" alt="Perspective at 25 mm with the help of a 0.7x conversion lens  [C-5050Z]" width="160" height="102"></a></td>
    </tr>
  </table>
</div>
<p>With this many variables in the mix, how best to play the distance vs. zoom
game can vary considerably from one shot to the next. Faces are usually much
more attractive in portraits taken through a long lens from some distance, and
you may achieve better <a href="#separation">background separation</a> to boot.
Wide-angle shots from close in tend to have more punch. Beyond that, you'll have
to use your judgment regarding perspective. If your digital camera has
a zoom lens, spend some time getting a feel for these trade-offs. Time will be
your only cost, and the experience will be worth a thousand words.</p>
<hr>
<h3><a name="andrzej"></a><b>Relating Digital to 35 mm Camera DOF</b></h3>
<p>Another excellent digital DOF reference is Andrzej Wrotniak's <a href="http://www.wrotniak.net/photo/dof/index.html">Depth
of field and your digital camera</a> page.&nbsp;Andrzej tells me that his DOF
calculations match his experience with an Oly C-3030Z quite well.</p>
<h4>Leveraging Film Experience with DOF</h4>
<p>For those already familiar with the
relationship between aperture settings and DOF in 35 mm cameras, Andrzej has
discovered a handy DOF conversion rule that applies to many currently available
2-5 MP
digital cameras:</p>
<div align="left">
  <table border="2">
    <tr>
      <td valign="top" align="left">
        <h3><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;<b>Andrzej
        Wrotniak's
        DOF Conversion Rule</b></h3>
      </td>
    </tr>
    <tr>
      <td valign="top" align="left">The depth of field afforded by a digital camera at
        a given f-stop is the same as that of a 35 mm camera with its aperture
        stopped down 5 more f-stops.</td>
    </tr>
  </table>
</div>
<p>Thus, at its f/4 <a href="#resolving">aperture sweet-spot</a>, my C-20x0Z's DOF
equals that of a 35 mm camera at f/22!</p>
<p>Like I said, DOF to burn.</p>
<h5>Technical Note: Andrzej's DOF work assumes a circle
of confusion of D/1440, where D is the effective CCD diagonal�in Andrzej's
case, 8.94 mm. See <a href="#dof_circle">below</a>,
however, for a discussion of circle issues in digital photography.</h5>

<table border="0">
    <tr>
        <td valign="top"><em><strong><a href="#motion"><img src="bypass.gif"
        alt="Marks opportunities to bypass long-winded discussions and cut to the action line. Click to review Limited Warranty section on the home page."
        align="texttop" border="0" width="36" height="30"></a></strong></em></td>
        <td valign="top">Click at left to skip to <a href="#motion">motion
          management</a> now. To learn about hyperfocal focusing in landscape
          work, read on.</td>
    </tr>
</table>

<div align="left">
  <table border="0" cellspacing="0" cellpadding="0">
    <tr>
      <td valign="bottom"></td>
      <td valign="bottom"></td>
      <td valign="bottom"></td>
    </tr>
    <tr>
      <td valign="bottom"><a href="index.htm#site_index"><img border="0" src="art_index.gif" width="133" height="34"></a></td>
      <td valign="bottom"><a href="#page_index"><img border="0" src="up.gif" width="41" height="51"></a></td>
      <td valign="bottom"><a href="filters.htm"><img border="0" src="next_art.gif" width="133" height="34"></a></td>
    </tr>
  </table>
</div>

<hr>

<h2><a name="hyperfocal"></a>Hyperfocal Technique</h2>

<h5><a href="c-2000z/checklists/index.htm#hyperfocal">Hyperfocal Checklist</a></h5>

<p>When it comes to shooting wide-angle landscapes with lots of foreground
interest (flowers, friends, etc.), you often need the closest possible near limit of DOF and a far limit
reliably at
infinity. The manual focusing method known as <i>hyperfocal technique</i> is
designed to give you just that.&nbsp;</p>

<p>At the heart of hyperfocal technique is the <i>hyperfocal
distance</i>, the distance to the nearest plane of acceptable focus when the
lens is focused at infinity. This is the distance h<sub>1</sub> already
encountered in the <a href="#dof_summary">DOF calculations</a> and <a href="#dof_thumb">digital
rules of thumb</a> above. As we saw there, a camera focused manually at a distance S<sub>o</sub>
= h<sub>1</sub> brings everything from h<sub>1</sub>/2 to infinity into
acceptable
focus. At wide-angle focal lengths, hyperfocal distances fall close enough to
the camera to allow a distant ridge, a flower a few
feet away and everything in between to be in good focus at once.</p>

<h4>What You'll Need</h4>

<p>To take advantage of hyperfocal technique in your landscapes, you'll need</p>

<ul>
  <li>
    <p style="margin-bottom: 9">a higher-end digital camera with an <i> accurately
    adjustable manual
focus</i> and some aperture adjustability</li>
  <li> hyperfocal settings and distances accurate for that camera.</li>
</ul>
<p>The following sections will help you get going.</p>

<h5>Technical Note: Of the two definitions of hyperfocal distance in common use, I
prefer
the one David Jacobsen adopts in his superb <a href="http://www.photo.net/photo/optics/lensTutorial.html">photo.net Lens Tutorial</a>.
His definition is used throughout this article.&nbsp;</h5>

<hr>

<h3><a name="hyperfocal_simple"></a>A Simplified Hyperfocal Technique</h3>

<h5><a href="c-2000z/checklists/index.htm#hyperfocal">Hyperfocal Checklist</a></h5>

<p>Here we'll work out an easy-to-use wide-angle hyperfocal technique
appropriate to your digital camera. If you already have a well-established <a href="#circle">circle of confusion</a> 
value (c) for your camera's image sensor, you're ready to start. If not, you may have to wade into the
<a href="#f_over_1000"> circle of
confusion quagmire</a> that follows this section before proceeding.</p>

<h4><a name="hyperfocal_custom"></a>Establishing Your Own Simplified Hyperfocal
Settings</h4>

<p>To hammer out a simplified hyperfocal method for any particular camera,</p>

<ul>
  <li>
    <p style="margin-bottom: 9">Determine <b> f</b><sub><b>min</b></sub>, the camera's
    widest-angle focal length. (This zoom setting will maximize the sweep of
    your hyperfocal shots.)</li>
  <li>
    <p style="margin-bottom: 9">Determine <b> N<sub>s</sub></b>, the f-number of the
    <a href="#resolving_sweet">maximum resolving power aperture</a> for your camera's lens. (This aperture will
    maximize image detail. If you're not sure, an f-number 1-2 full stops down
    from wide open is a good assumption.)&nbsp;</li>
  <li>
    <p style="margin-bottom: 9">Determine <b>c</b>, the <a href="#confusion">circle of confusion</a> 
    value appropriate for your camera's sensor and for the image quality you
    desire. (As explained below, the value of c represents a sensor-specific criterion for
    &quot;acceptably sharp&quot; focus. If you don't have a reliable value for c, try c = D/1260, where D is your
camera sensor's diagonal in millimeters.)</li>
  <li>
    <p style="margin-bottom: 9">Use the formula below to calculate your camera's
    <i>simplified hyperfocal distance</i>  <b> h<sub>1s</sub> </b> and near
    limit of DOF <b> h<sub>1s</sub>/2</b>.
        <p style="margin-bottom: 9"><b>h<sub>1s</sub> = f<sub>min</sub><sup>2</sup> / (N<sub>s</sub> * c)</b></li>
  <li>
    <p style="margin-bottom: 9">Work out a reproducible way to achieve an <a href="#manual_focus">accurate
    manual focus</a> at <b> h<sub>1s</sub></b>. For some cameras, this may be
    the most challenging step.</li>
  <li>
    <p style="margin-bottom: 9"><i><b>Test your results against the final image as
    you intend it to be viewed.</b></i> With a properly chosen circle value c, your far limit of DOF should
    reach infinity and your near limit should
    fall at h<sub>1s</sub>/2 when you're manually focused at h<sub>1s</sub>. All
    objects falling in between should be acceptably sharp when printed or
    otherwise viewed as intended. If not, you've either
    <ul>
      <li>
        <p style="margin-bottom: 9">chosen an incorrect <a href="#circle">circle
        of confusion</a> value c for the calculation,</li>
      <li>
        <p style="margin-bottom: 9">managed to focus at some distance other than
        h<sub>1s</sub>, or</li>
      <li>
        <p style="margin-bottom: 9">used an asymmetrical lens (a <a href="c-2000z/lenses/index.htm">wide-angle
        conversion lens</a>, perhaps) with significantly different entrance and
        exit pupils (i.e., p &lt;&gt; 1).</li>
    </ul>
  </li>
</ul>
<blockquote>
    <p style="margin-bottom: 9">Tweak c
    or your manual focusing technique or try another lens as needed and repeat Steps 3-6 until you get
    results yield the desired image quality.
</blockquote>
<ul>
  <li>
    <p style="margin-bottom: 9">Once you've confirmed good empirical values for c and h<sub>1s</sub>, record your
hyperfocal camera settings (f<sub>min</sub>, N<sub>s</sub>) and the distances h<sub>1s</sub>
    and h<sub>1s</sub>/2 on a card and drop it into your camera bag
for future use. Better yet, if your camera allows you to store detailed camera
    configurations (as does the C-5050Z), set your zoom to widest angle f<sub>min</sub>,
    your aperture to N<sub>s</sub>, and manual focus at h<sub>1s</sub> and store
    the configuration.</li>
</ul>
<p>Now you're ready to put your tested hyperfocal settings to work.&nbsp;</p>

<h4><a name="hyperfocal_field"></a>Simplified Hyperfocal Technique in the Field</h4>

<p>To use hyperfocal technique in the field, just follow these steps:</p>

<ol>
  <li>
    <p style="margin-bottom: 9">Zoom out to full wide-angle (f<sub>min</sub>).</li>
  <li>
    <p style="margin-bottom: 9">Dial in your sweet-spot f-number (N<sub>s</sub>).</li>
  <li>
    <p style="margin-bottom: 9">Focus manually at the corresponding simplified hyperfocal distance h<sub>1s</sub>.&nbsp;
  </li>
  <li>
    <p style="margin-bottom: 9">Position your camera to place the nearest
    in-focus foreground object
    at or slightly beyond a distance <b>h<sub>1s</sub> / 2</b> from the camera.&nbsp;</li>
  <li>
    <p style="margin-bottom: 9">Make any other camera adjustments warranted by
    the scene.</li>
  <li>
    <p style="margin-bottom: 9">Fire away.</li>
</ol>
<p>That's all there is to it.</p>

<h4><a name="circle"></a>Determining Your Sensor's Circle of Confusion</h4>

<p> The circle of confusion right for your camera depends largely on the
properties of its sensor. If you don't have a reliable value for c, try c = D/1260, where D is
the sensor's diagonal in millimeters. (Sensor dimensions are often given in
the specifications listed in your camera's manual. Failing that, look up your
camera in the side-by-side section at <a href="http://www.dpreview.com">Digital
Photography Review</a>.)&nbsp; Alternatively, try the circle associated
    with the sample camera from the table below best matching your sensor's type
and maximum resolution.&nbsp;If you're ready to delve into the many ways one
might reasonably determine c for a digital camera, take a deep breath and click <a href="#dof_circle">here</a>.</p>

  <table border="2">
    <tr>
      <td valign="top" align="left" width="1050" colspan="4">
        <h3>Simplified Hyperfocal Settings for Oly C-2020Z, C-3030Z and
        C-5050Z&nbsp;Cameras</h3>
      </td>
    </tr>
    <tr>
      <td valign="top" align="left" width="300"><b>Specs and Settings</b></td>
      <td valign="top" align="left" width="236"><b>C-2020Z</b> (2MP, f/2.0)&nbsp;</td>
      <td valign="top" align="left" width="257"><b>C-3030Z</b>  (3.3MP, f/2.8)<b>&nbsp;</b></td>
      <td valign="top" align="left" width="257"><b>C-5050Z</b>  (5.2MP, f/1.8)<b>&nbsp;</b></td>
    </tr>
    <tr>
      <td width="300">Sensor type </td>
      <td align="right" width="236">1/2&quot;</td>
      <td align="right" width="257">1/1.8&quot;</td>
      <td align="right" width="257">1/1.8&quot;</td>
    </tr>
    <tr>
      <td width="300">Sensor diagonal </td>
      <td align="right" width="236">8.0 mm</td>
      <td align="right" width="257">8.94 mm</td>
      <td align="right" width="257">8.94 mm</td>
    </tr>
    <tr>
      <td width="300">Sensel width </td>
      <td align="right" width="236">0.0039 mm</td>
      <td align="right" width="257">0.00345 mm</td>
      <td align="right" width="257">0.00281 mm</td>
    </tr>
    <tr>
      <td width="300">Widest-angle focal length, f<sub>min</sub> </td>
      <td align="right" width="236"> 6.5 mm</td>
      <td align="right" width="257"> 6.5 mm</td>
      <td align="right" width="257"> 7.1 mm</td>
    </tr>
    <tr>
      <td width="300"><a href="#resolving_sweet">Sweet-spot</a> <a href="#f-number"> f-number</a>, N<sub>s</sub>&nbsp;</td>
      <td align="right" width="236">4.0</td>
      <td align="right" width="257">5.6</td>
      <td align="right" width="257">4.0</td>
    </tr>
    <tr>
      <td width="300">Circle of confusion, c</td>
      <td align="right" width="236">0.0093 mm</td>
      <td align="right" width="257">0.0071 mm</td>
      <td align="right" width="257">0.0071 mm</td>
    </tr>
    <tr>
      <td width="300">Circle source</td>
      <td align="left" width="236">C-2000Z DOF tables</td>
      <td align="left" width="257"><a href="#g1_circle">Canon G1 settings</a></td>
      <td align="left" width="257"><a href="#g1_circle">Canon G1 settings</a></td>
    </tr>
    <tr>
      <td width="300"><b>Focusing distance, h<sub>1s</sub></b></td>
      <td align="right" width="236"><b>1.14 m = 3.74 ft</b></td>
      <td align="right" width="257"><b>1.06 m = 3.47 ft&nbsp;</b></td>
      <td align="right" width="257"><b>1.76 m = 5.82 ft</b></td>
    </tr>
    <tr>
      <td width="300">Near limit of DOF, h<sub>1s</sub>/2</td>
      <td align="right" width="236">0.57 m = 1.87 ft&nbsp;</td>
      <td align="right" width="257">0.53 m = 1.73 ft</td>
      <td align="right" width="257">0.89 m = 2.91 ft</td>
    </tr>
    <tr>
      <td width="300">Far limit of DOF</td>
      <td align="right" width="236">infinity</td>
      <td align="right" width="257">infinity</td>
      <td align="right" width="257">infinity</td>
    </tr>
  </table>
<p>In these samples, focusing at h<sub>1s</sub> brings everything from slightly over half a meter to infinity
into acceptably sharp focus � from the flowers at your feet to the mountain on the horizon.</p>

<h4><a name="manual_focus"></a>Manual Focus Via Auto-focus</h4>

<p>Establishing an accurate manual focus at the hyperfocal distance (in this
case, h<sub>1s</sub>) is critical to the success of any hyperfocal technique.
Failure to do so may result in blurring of your closest or farthest subjects, if
not both, especially if you happen to focus too close in.</p>

<p>If your manual focus scale is as inaccurate and difficult to interpolate as
mine (on both the C-2020Z and the C-5050Z), you might try <a href="http://www.wrotniak.com/photo/c5050/c5050-leica.html">Andrzej
Wrotniak's autofocus (AF) trick for the C-5050Z</a> if your camera has similar
features.&nbsp;</p>

<ol>
  <li>
    <p style="margin-bottom: 9">Pick an easy AF target � one with little
    depth, some vertical lines and no glare.&nbsp;</li>
  <li>
    <p style="margin-bottom: 9">Position yourself an exact distance h<sub>1s</sub>
    from the target using a tape measure.</li>
  <li>
    <p style="margin-bottom: 9">Set your camera for AF at f<sub>min</sub>
    and&nbsp; N<sub>s</sub>, aim at the target and half-press the shutter
    release until you get a green light indicating a good focus. (If the camera
    has to hunt for a focus, pick another target.)</li>
  <li>
    <p style="margin-bottom: 9">With the shutter release still half-pressed,
    press the focus mode button. This will transfer the focus distance to manual
    focus.&nbsp;</li>
  <li>
    <p style="margin-bottom: 9">Note the position of the distance indicator on
    the manual focus scale. Better yet, save f<sub>min</sub> and&nbsp; N<sub>s</sub>,
    and the manual focus at h1s in one of your &quot;My Mode&quot; slots.</li>
</ol>
<p>If that doesn't work for your camera, do anything you have to do to get an
accurate manual focus at h<sub>1s</sub>.</p>

<h4>Departing from f<sub>min</sub>, N<sub>s</sub> and h<sub>1s</sub></h4>

<p>Now that you have a workable but highly constrained hyperfocal technique in
hand, it's worth knowing how to stray from it safely. The hyperfocal equation h<sub>1</sub> =
f<sup>2</sup> / (N * c) points the way.</p>

<p>Luckily, anything that <i>decreases</i> h<sub>1</sub> can be done safely
without departing from the S<sub>o</sub> = h<sub>1s</sub> manual focus setting
determined <a href="#hyperfocal_custom">above</a>. Narrowing the aperture
(increasing N) is the cleanest example. Mounting a wide-angle converter to reach
a focal length below f<sub>min</sub> might also qualify, but note <a href="#hyperfocal_caveats">this
lens-related caveat</a>
before relying on it.</p>

<p>Now for the bad news.&nbsp;</p>

<table border="0">
    <tr>
        <td valign="top"><a href="index.htm#warranty"><em><strong><img src="tumbling_arrow.gif" alt="Marks the gotchas" align="left" border="0" hspace="0" width="16" height="16"></strong></em></a></td>
        <td valign="top"><b><i>Zooming in from </i></b> f<sub>min </sub><b><i>or
          changing the aperture
          from </i></b>N<sub>s</sub><b><i> can cause severe hyperfocal failures, both near and far.</i></b></td>
    </tr>
</table>

<p>If you stay focused at S<sub>o</sub> =&nbsp; h<sub>1s</sub>, any adjustment
that pushes h<sub>1</sub> out beyond h<sub>1s</sub> puts both near and far focus
at risk.</p>

<p>Because it's squared in h<sub>1</sub> = f<sup>2</sup> / (N * c), focal length
will always be your tightest constraint. Without a fully offsetting increase in N,
zooming in beyond the f<sub>min</sub> used to calculate your h<sub>1s</sub> is a
sure recipe for disaster if you're still focused at h<sub>1s</sub>. Note that
doubling f would require an offsetting 2-stop (four-fold) increase N to keep h1 at h<sub>1s</sub>!</p>

<p>Opening up the aperture also pushes h<sub>1</sub> away in inverse proportion
to N. If you're still focused at h<sub>1s</sub>, both near and far focus can be
lost at N &gt; N<sub>s</sub>. Note that h<sub>1</sub> doubles for every 2-stop
(twofold) decrease in N.</p>

<p>Finally, at f<sub>min</sub> and N<sub>s</sub>, focusing at S<sub>o</sub> &gt;
h<sub>1s</sub> will maintain distant focus, but the near limit of DOF will move
out accordingly, and your closest subjects may well end up blurred � hence the
importance of an <a href="#manual_focus">accurate manual focus</a> at h<sub>1s</sub>.
The only real hyperfocal
implementation challenge on my C-2020Z and C-5050Z cameras are their highly
inaccurate and nonlinear manual focus
distance scales. Dialing in 1.14 m between
the 0.8 m and 2 m marks requires an act of faith. To work around the scale on
his C-5050Z, Andrzej Wrotniak uses automatic focus to establish
an accurate focus on a test object at the S<sub>o</sub> before transferring the
result to manual focus, as summarized <a href="#manual_focus">above</a> and
described in detail at <a href="http://www.wrotniak.com/photo/c5050/c5050-leica.html">Use
Your C-5050Z/C-5060WZ Like a Leica</a>.</p>

<blockquote>
  <p><b><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;When in
  doubt, focus beyond h<sub>1s</sub> and count on a near limit of DOF farther
  away than h<sub>1s</sub>/2.</b></p>

</blockquote>
<p>This strategy maintains distant focus at the expense of the near limit of
DOF, but stepping back a few feet to accommodate the latter usually beats moving
up a mile to get that distant ridge back in focus.</p>

<p>Note that the &quot;pan-focus&quot; hyperfocal mode built into the 3MP Canon PowerShot G1 (see Fini Jastrow's
description <a href="#g1_circle">below</a>) eliminates such manual focus
uncertainties. The G1 uses hyperfocal settings similar to those shown for the
3MP C-30x0Z and achieves similar results.&nbsp;</p>

<h5><b><a name="hyperfocal_caveats"></a>Technical Note:</b> All hyperfocal
calculations in this article assume (1) symmetrical lenses (p = pupil magnification
= exit pupil / (entrance pupil
= 1) and (2) a subject-to-lens distance S<sub>o</sub> many times
the <i>actual</i>
focal length (i.e., S<sub>o</sub>  &gt;&gt; f). These are probably a good bets for your digital zoom lens, but
they're not guaranteed, particularly with regard to p. If you can't find a workable value of c for your camera, p may be
less than 1 at f<sub>min</sub>.&nbsp;A wide-angle converter might also make p
&lt; 1. The hyperfocal distance notation h<sub>1</sub>  used here serves as a reminder of
the p = 1 assumption. With typical digital camera focal lengths of 20 mm or less,
the
approximation f � S<sub>o</sub> almost always holds up in the field. For a more
general treatment of DOF allowing for asymmetric lenses, see <a href="http://www.vanwalree.com/optics/dofderivation.html">Paul
Van Walree's photography &amp; optics</a>.</h5>

<table border="0">
    <tr>
        <td valign="top"><em><strong><a href="#motion"><img src="bypass.gif"
        alt="Marks opportunities to bypass long-winded discussions and cut to the action line. Click to review Limited Warranty section on the home page."
        align="texttop" border="0" width="36" height="30"></a></strong></em></td>
        <td valign="top">Click at left to skip to <a href="#motion">motion
          management</a>. To revel in the intricacies of hyperfocal
          calculations and circle of confusion issues, read on.</td>
    </tr>
</table>

<hr>

<h3><b><a name="hyperfocal_calc"></a>Hyperfocal Calculations</b></h3>

<p>For so-called symmetrical lenses with equal entrance and exit pupils (generally all but wide-angle lenses), hyperfocal distance depends on focal length, aperture
and the desired degree of sharpness according to&nbsp;</p>
<div align="left">
  <blockquote>
    <table border="0">
      <tr>
        <td><b>h<sub>1</sub></b></td>
        <td><b> =&nbsp; f</b><sup><b>2</b></sup><b> / (N * c)</b></td>
      </tr>
      <tr>
        <td></td>
        <td><b> = (f<sub>35</sub> / FLR<sub>35</sub>)</b><sup><b>2</b></sup><b> /
  (N * c)</b></td>
      </tr>
    </table>
  </blockquote>
</div>
<p>where</p>
<ul>
  <li>
    <p style="margin-bottom: 9">h<sub>1</sub> = the hyperfocal distance,</li>
  <li>
    <p style="margin-bottom: 9">f = the actual focal length</li>
  <li>
    <p style="margin-bottom: 9">f<sub>35</sub> = equivalent focal
    length (EFL) in a 35 mm camera</li>
  <li>
    <p style="margin-bottom: 9">FLR<sub>35</sub> = f<sub>35</sub> / f ~ D<sub>35</sub> /
    D = 43.3 / D, where D<sub>35</sub>  is the diagonal of the 35 mm frame and D
    is your sensor diagonal, both in mm</li>
  <li>
    <p style="margin-bottom: 9">N = aperture <a href="#f-number"> f-number</a>
(e.g., the 2.8 in f/2.8)</li>
  <li>
    <p style="margin-bottom: 9">c is the maximum acceptable <a href="#dof_circle"> circle of
    confusion</a></li>
</ul>
<p>Once again, all lengths must use the same units, usually in mm.</p>

<p><a name="flr35"></a>You can calculate the constant FLR<sub>35 </sub> = f<sub>35</sub> / f for your camera's main lens at any zoom setting for which you have reliable
data relating f<sub>35</sub> and f � e.g., from your camera's lens specifications.
Note that FLR<sub>35 </sub>  depends only on sensor diagonal and therefore on
sensor type. For the 1/2&quot; type CCD in the C-2020Z, FLR<sub>35</sub> is 5.385, while it's 4.923 for 1/1.8&quot; type CCDs
in the
C-3030Z, C-4040Z and C-5050Z. In fact, for most currently available 2-5MP cameras, FLR<sub>35</sub> is
reasonably close to
5.</p>

<h5><b>Technical Note:</b>  When&nbsp; f � S<sub>o</sub>, FLR<sub>35</sub>  then reduces
to 43.3 / D, where 43.3 mm is the diagonal of the 35 mm camera frame
and D is your effective sensor diagonal in mm. With typical digital camera focal lengths of 20 mm or less,
the approximation f � S<sub>o</sub>  ( S<sub>o</sub> &gt; 10 * f is good
enough) would break down in practice only in extreme macro shots, if then.</h5>

<hr>

<h3><a name="hyperfocal_table"></a><b>Sample Hyperfocal Table for
the Oly C-2020Z</b></h3>

<p>The table below gives sample hyperfocal distances for my C-2020Z calculated
from h<sub>1</sub> =&nbsp; f<sup>2</sup> / (N * c) and a reasonable c = 0.0093 mm
from the discussion <a href="#circle_du_jour">below</a>.</p>

<table border="0">
    <tr>
        <td valign="top"><a href="index.htm#warranty"><em><strong><img src="tumbling_arrow.gif" alt="Marks the gotchas" align="left" border="0" hspace="0" width="16" height="16"></strong></em></a></td>
        <td valign="top"><b><i>This table depends critically on c, the chosen circle of
          confusion.</i></b></td>
    </tr>
</table>

<p>Whether the table produces accurately focused images remains to be seen,
but at least I've shown my work. As soon as I figure out a workable and
reliable method, I plan to test these numbers in the field. The major stumbling
block is the very non-linear manual focus scale of unknown accuracy found in
most Oly C-series cameras. I
may have to calibrate the scale first, and that'll take some doing.&nbsp;</p>
<table border="2" width="614">
  <col width="99" style="mso-width-source:userset;mso-width-alt:3527;width:74pt">
  <col width="64" span="5" style="width:48pt">
  <tr height="18" style="height:13.2pt">
    <td colspan="6" style="height: 13.2pt; mso-ignore: colspan" width="790" valign="top">
      <h4>Hyperfocal Distances h<sub>1</sub> (mm) for the Oly C-20x0Z</h4>
    </td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" style="height: 13.2pt" width="665" valign="top" colspan="6">Based
      on a 0.0093 mm <a href="#circle_du_jour">circle of confusion</a></td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" style="height: 13.2pt" width="219" valign="top">Converter
      lens</td>
    <td width="89" valign="top"><b>0.8x (Oly&nbsp; B-28)</b></td>
    <td width="89" valign="top"><b>None</b></td>
    <td width="89" valign="top"><b>None</b></td>
    <td width="89" valign="top"><b>None</b></td>
    <td width="90" valign="top"><b>1.7x (Oly B-300)</b></td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" style="height: 13.2pt" width="219" valign="top">Zoom factor</td>
    <td align="right" x:num="00.8" width="89" valign="top">0.8</td>
    <td align="right" x:num width="89" valign="top">1.0</td>
    <td align="right" x:num width="89" valign="top">2.0</td>
    <td align="right" x:num width="89" valign="top">3.0</td>
    <td align="right" x:num x:fmla="=E4*1.7" width="90" valign="top">5.1</td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" style="height: 13.2pt" width="219" valign="top">Final f (mm)</td>
    <td align="right" x:num x:fmla="=$C$5*B4" valign="top" width="89">5.2</td>
    <td align="right" x:num valign="top" width="89">6.5</td>
    <td align="right" x:num x:fmla="=$C$5*D4" valign="top" width="89">13.0</td>
    <td align="right" x:num x:fmla="=$C$5*E4" valign="top" width="89">19.5</td>
    <td align="right" x:num x:fmla="=$C$5*F4" valign="top" width="90">33.2</td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" style="height: 13.2pt" width="219" valign="top">Final f<sub>35</sub>
      (mm)</td>
    <td align="right" x:num x:fmla="=$C$5*B4" valign="top" rowspan="2" width="89">28</td>
    <td align="right" x:num valign="top" rowspan="2" width="89">35</td>
    <td align="right" x:num x:fmla="=$C$5*D4" valign="top" rowspan="2" width="89">70</td>
    <td align="right" x:num x:fmla="=$C$5*E4" valign="top" rowspan="2" width="89">105</td>
    <td align="right" x:num x:fmla="=$C$5*F4" valign="top" rowspan="2" width="90">178.5</td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" class="xl25" align="right" style="height: 13.2pt" x:num width="219" valign="top">
      <p align="left"><b>F-number N&nbsp;</b></td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" class="xl25" align="right" style="height: 13.2pt" x:num width="219" valign="top">2.0</td>
    <td class="xl24" align="right" x:num="1456" width="89" valign="top">1,456</td>
    <td class="xl24" align="right" x:num="2275" width="89" valign="top">2,275</td>
    <td class="xl24" align="right" x:num="9100" width="89" valign="top">9,100</td>
    <td class="xl24" align="right" x:num="20475" width="89" valign="top">20,475</td>
    <td class="xl24" align="right" x:num="59172.75" width="90" valign="top">59,173</td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" class="xl25" align="right" style="height: 13.2pt" x:num width="219" valign="top">2.2</td>
    <td class="xl24" align="right" x:num="1323.6363636363631" width="89" valign="top">1,324</td>
    <td class="xl24" align="right" x:num="2068.1818181818171" width="89" valign="top">2,068</td>
    <td class="xl24" align="right" x:num="8272.7272727272684" width="89" valign="top">8,273</td>
    <td class="xl24" align="right" x:num="18613.63636363636" width="89" valign="top">18,614</td>
    <td class="xl24" align="right" x:num="53793.409090909081" width="90" valign="top">53,793</td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" class="xl25" align="right" style="height: 13.2pt" x:num width="219" valign="top">2.5</td>
    <td class="xl24" align="right" x:num="1164.8" width="89" valign="top">1,165</td>
    <td class="xl24" align="right" x:num="1820" width="89" valign="top">1,820</td>
    <td class="xl24" align="right" x:num="7280" width="89" valign="top">7,280</td>
    <td class="xl24" align="right" x:num="16380" width="89" valign="top">16,380</td>
    <td class="xl24" align="right" x:num="47338.2" width="90" valign="top">47,338</td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" class="xl25" align="right" style="height: 13.2pt" x:num width="219" valign="top">2.8</td>
    <td class="xl24" align="right" x:num="1040" width="89" valign="top">1,040</td>
    <td class="xl24" align="right" x:num="1625" width="89" valign="top">1,625</td>
    <td class="xl24" align="right" x:num="6500" width="89" valign="top">6,500</td>
    <td class="xl24" align="right" x:num="14625" width="89" valign="top">14,625</td>
    <td class="xl24" align="right" x:num="42266.25" width="90" valign="top">42,266</td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" class="xl25" align="right" style="height: 13.2pt" x:num width="219" valign="top">3.2</td>
    <td class="xl24" align="right" x:num width="89" valign="top">910</td>
    <td class="xl24" align="right" x:num="1421.875" width="89" valign="top">1,422</td>
    <td class="xl24" align="right" x:num="5687.5" width="89" valign="top">5,688</td>
    <td class="xl24" align="right" x:num="12796.874999999998" width="89" valign="top">12,797</td>
    <td class="xl24" align="right" x:num="36982.968749999993" width="90" valign="top">36,983</td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" class="xl25" align="right" style="height: 13.2pt" x:num width="219" valign="top">3.6</td>
    <td class="xl24" align="right" x:num="808.88888888888857" width="89" valign="top">809</td>
    <td class="xl24" align="right" x:num="1263.8888888888882" width="89" valign="top">1,264</td>
    <td class="xl24" align="right" x:num="5055.5555555555529" width="89" valign="top">5,056</td>
    <td class="xl24" align="right" x:num="11375" width="89" valign="top">11,375</td>
    <td class="xl24" align="right" x:num="32873.75" width="90" valign="top">32,874</td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" class="xl25" align="right" style="height: 13.2pt" x:num width="219" valign="top">4.0</td>
    <td class="xl24" align="right" x:num width="89" valign="top">728</td>
    <td class="xl24" align="right" x:num="1137.5" width="89" valign="top">1,138</td>
    <td class="xl24" align="right" x:num="4550" width="89" valign="top">4,550</td>
    <td class="xl24" align="right" x:num="10237.5" width="89" valign="top">10,238</td>
    <td class="xl24" align="right" x:num="29586.374999999996" width="90" valign="top">29,586</td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" class="xl25" align="right" style="height: 13.2pt" x:num width="219" valign="top">4.5</td>
    <td class="xl24" align="right" x:num="647.11111111111086" width="89" valign="top">647</td>
    <td class="xl24" align="right" x:num="1011.1111111111107" width="89" valign="top">1,011</td>
    <td class="xl24" align="right" x:num="4044.444444444443" width="89" valign="top">4,044</td>
    <td class="xl24" align="right" x:num="9100" width="89" valign="top">9,100</td>
    <td class="xl24" align="right" x:num="26299" width="90" valign="top">26,299</td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" class="xl25" align="right" style="height: 13.2pt" x:num width="219" valign="top">5.0</td>
    <td class="xl24" align="right" x:num="582.4" width="89" valign="top">582</td>
    <td class="xl24" align="right" x:num width="89" valign="top">910</td>
    <td class="xl24" align="right" x:num="3640" width="89" valign="top">3,640</td>
    <td class="xl24" align="right" x:num="8190" width="89" valign="top">8,190</td>
    <td class="xl24" align="right" x:num="23669.1" width="90" valign="top">23,669</td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" class="xl25" align="right" style="height: 13.2pt" x:num width="219" valign="top">5.6</td>
    <td class="xl24" align="right" x:num width="89" valign="top">520</td>
    <td class="xl24" align="right" x:num="812.5" width="89" valign="top">813</td>
    <td class="xl24" align="right" x:num="3250" width="89" valign="top">3,250</td>
    <td class="xl24" align="right" x:num="7312.5" width="89" valign="top">7,313</td>
    <td class="xl24" align="right" x:num="21133.125" width="90" valign="top">21,133</td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" class="xl25" align="right" style="height: 13.2pt" x:num width="219" valign="top">6.0</td>
    <td class="xl24" align="right" x:num="485.3333333333332" width="89" valign="top">485</td>
    <td class="xl24" align="right" x:num="758.33333333333303" width="89" valign="top">758</td>
    <td class="xl24" align="right" x:num="3033.3333333333321" width="89" valign="top">3,033</td>
    <td class="xl24" align="right" x:num="6825" width="89" valign="top">6,825</td>
    <td class="xl24" align="right" x:num="19724.25" width="90" valign="top">19,724</td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" class="xl25" align="right" style="height: 13.2pt" x:num width="219" valign="top">7.0</td>
    <td class="xl24" align="right" x:num width="89" valign="top">416</td>
    <td class="xl24" align="right" x:num width="89" valign="top">650</td>
    <td class="xl24" align="right" x:num="2600" width="89" valign="top">2,600</td>
    <td class="xl24" align="right" x:num="5850" width="89" valign="top">5,850</td>
    <td class="xl24" align="right" x:num="16906.5" width="90" valign="top">16,907</td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" class="xl25" align="right" style="height: 13.2pt" x:num width="219" valign="top">8.0</td>
    <td class="xl24" align="right" x:num width="89" valign="top">364</td>
    <td class="xl24" align="right" x:num="568.75" width="89" valign="top">569</td>
    <td class="xl24" align="right" x:num="2275" width="89" valign="top">2,275</td>
    <td class="xl24" align="right" x:num="5118.75" width="89" valign="top">5,119</td>
    <td class="xl24" align="right" x:num="14793.187499999998" width="90" valign="top">14,793</td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" class="xl25" align="right" style="height: 13.2pt" x:num width="219" valign="top">9.0</td>
    <td class="xl24" align="right" x:num="323.55555555555543" width="89" valign="top">324</td>
    <td class="xl24" align="right" x:num="505.55555555555537" width="89" valign="top">506</td>
    <td class="xl24" align="right" x:num="2022.2222222222215" width="89" valign="top">2,022</td>
    <td class="xl24" align="right" x:num="4550" width="89" valign="top">4,550</td>
    <td class="xl24" align="right" x:num="13149.5" width="90" valign="top">13,150</td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" class="xl25" align="right" style="height: 13.2pt" x:num width="219" valign="top">10.0</td>
    <td class="xl24" align="right" x:num="291.2" width="89" valign="top">291</td>
    <td class="xl24" align="right" x:num width="89" valign="top">455</td>
    <td class="xl24" align="right" x:num="1820" width="89" valign="top">1,820</td>
    <td class="xl24" align="right" x:num="4095" width="89" valign="top">4,095</td>
    <td class="xl24" align="right" x:num="11834.55" width="90" valign="top">11,835</td>
  </tr>
  <tr height="18" style="height:13.2pt">
    <td height="18" class="xl25" align="right" style="height: 13.2pt" x:num width="219" valign="top">11.0</td>
    <td class="xl24" align="right" x:num="264.72727272727263" width="89" valign="top">265</td>
    <td class="xl24" align="right" x:num="413.63636363636346" width="89" valign="top">414</td>
    <td class="xl24" align="right" x:num="1654.5454545454538" width="89" valign="top">1,655</td>
    <td class="xl24" align="right" x:num="3722.7272727272725" width="89" valign="top">3,723</td>
    <td class="xl24" align="right" x:num="10758.681818181816" width="90" valign="top">10,759</td>
  </tr>
</table>

<p>Andrzej Wrotniak has posted DOF tables for several Oly C-series and E-series
cameras based on a D/1440 circle of confusion. See, for example, his worthwhile article <a href="http://www.wrotniak.net/photo/dof/index.html">Depth of
field and your digital camera</a>. Andrzej states that the calculated distances stand up to his
field testing.</p>

<hr>

<h3><b><a name="dof_circle"></a>Pick a Circle, Any Circle</b></h3>

<p>It's easy enough to generate hyperfocal distance tables like the one <a href="#hyperfocal_table">above</a>
with a spreadsheet and the standard hyperfocal equation h =&nbsp; f<sup>2</sup> / (N * c).
Generating a table that actually yields properly focused images is
another story. The hard part is choosing the right <i>circle of confusion</i> 
(c), the standard
measure of &quot;acceptable sharpness&quot; in photographs. I won't go into a
precise definition of c here, but it's basically the diameter of the circular image
that an imperfectly focused point subject would form at the image receiver plane. You'll find good discussions in David Jacobsen's <a href="http://www.photo.net/photo/optics/lensTutorial.html">photo.net Lens Tutorial</a>.
Note that having a <i>realistic</i> value for c is a necessary starting point in
any <a href="#dof_summary">DOF
calculation</a>, hyperfocal or otherwise.</p>

<p>Film photographers have developed a number of workable circle of confusion rules,
all ultimately tied to the diagonal of the image receiver considered to be
continuous in nature. These include</p>

<p>working backward from end-use quality requirements</p>

<p>taking c as a fraction of the frame diagonal D � e.g., c = D/1440</p>

<p>using c = f/1000, where f is either the normal or actual focal length</p>

<p>approaches. Unfortunately, they all yield different results.&nbsp;</p>

<p>On the digital side, the discrete <i>sensels</i> (light
sensing elements) of the CCD or CMOS sensor, the anti-aliasing filter applied
to the sensor, and the color interpolation and sharpening schemes eventually
applied to the image data all potentially complicate the choice, but few
treatments of digital c values tackle those complications head-on. To my
knowledge, the only circle of confusion rule unique to digital photography is
the <a href="#twice">twice sensel size rule</a> discussed below. It is also the
only rule that doesn't rely on the sensor diagonal.</p>

<h4><a name="end-quality"></a>The End-Quality Approach</h4>

<p>The most straightforward approach to establishing a circle of confusion diameter
(c) is to work backward from
desired output image quality to find the c required. We'll take as our output
image a 10x7.5&quot; (4:3) print with a diagonal of 12.5&quot; or 318 mm, and
for the moment, we'll ignore pesky printing details like desired number of
pixels per inch.&nbsp;</p>

<p>The human <a href="vision.htm#brain-eye">brain-eye system</a> considers a print sharp
when c is magnified in the final image to no more than 0.25 mm (0.01&quot;),
the width spanned by the eye's maximum angular resolution of ~2 arc minutes at a
viewing distance of 430 mm (17&quot;). Details measuring 0.25 mm or less can't
be resolved at 430 mm or farther out, whether blurred or sharp, but if you
anticipate closer viewing, c will have to be commensurately smaller at the
camera end.</p>

<p>Now let's calculate the magnification M necessary to produce our 10&quot;
print. The
diagonals of most consumer-grade 4:3 CCD and CMOS sensors fall in the 8-11 mm
range, with the 8.94 mm diagonal of 1/1.8&quot; type 3-5MP CCDs being perhaps
the most common as of 2Q2004. To reach the 318 mm diagonal of our final print,
we'd need to magnify the CCD diagonal by M = 318 / 8.94 = 35.5x. And to end up
with a magnified circle of confusion of 0.25 mm on paper, we'd need to start
with a 0.25/35.5 = 0.0070 mm = D/1272 circle at the CCD. We'd get the same c
value for 1/1.8&quot; type 5.2 MP CCD in my Oly C-5050Z because its diameter
equals that of the 1/1.8&quot; type 3.3MP sensor.</p>

<p>Thus, for all 1/1.8&quot; type sensors,&nbsp;</p>

<div align="left">
  <table border="0">
    <tr>
      <td>c</td>
      <td>= D * c<sub>print</sub> / D<sub>print</sub></td>
    </tr>
    <tr>
      <td></td>
      <td>= 8.94 mm * 0.25 mm / 318 mm</td>
    </tr>
    <tr>
      <td></td>
      <td>= 0.0070 mm = D/1272</td>
    </tr>
  </table>
</div>
<p>where c and D without subscripts refer to the sensor.</p>

<p>Encouragingly, this c value is very close to the 0.0071 mm circle Canon
adopted for the <a href="#g1_circle">&quot;pan-focus&quot;</a>
hyperfocal mode built into its G1 digital rangefinder. It also
happens to be very close to <a href="#twice"> twice sensel size</a> (0.00354 mm)
for the G1's 1/1.8&quot; type 3.3MP CCD, but it's considerably larger than the <a href="#twice"> twice the sensel
size</a> c value of 0.0056 mm for the 1/1.8&quot; type 5.52MP sensor.</p>

<p>Note that this end-use approach depends solely on the viewing circle demanded
for the print and the ratio of print and sensor diagonals, with no implicit or
explicit reference to sensel count.</p>

<h4>The Printer Factor</h4>

<p>Now, all of this would be fine and dandy for a film print, where the
effective pixel size is the ~1 micron diameter of a silver halide or dye grain.
But what about digital prints? A 10&quot; print from the G1's 3.3MP sensor would
have a maximum horizontal resolution of 2046 pixels and a printer resolution of
2046 / 10 = 205 ppi (pixels per inch). Those who insist on 250-300 ppi for their
prints would consider such a 10&quot; print to be limited by its printer
resolution � more perhaps than by quality of focus. With a 1/1.8&quot; type
5.2MP CCD with the same diagonal, the required circle would stay the same, but
now we'd have a horizontal resolution of 2560 pixels and a 10&quot; print
resolution of 256 dpi. At 256 ppi, small deviations from acceptable sharpness
due to focus should be visible.</p>

<h4><a name="f_over_1000"></a>The &quot;f/1000&quot; Approach</h4>

<p>Many other circle of confusion approaches are possible. Let's continue to ignore the untidy digital
complications and forge a
circle now using a widely-accepted film-based &quot;f/1000&quot; approach. I have <a href="#reservations">reservations</a>
about the general applicability of this approach on the
digital side, but for now, let's see where it leads.</p>
<p><a name="kodak"></a>For any photographic format, the venerable <i>Kodak
Professional Photoguide</i> states,</p>
<blockquote>
  <p>&quot;The size of the circle of confusion used to calculate depth of field
  is about 1/1000 of the focal length of the <i>normal</i> focal length lens for
  each [image] format.&quot; [emphasis mine]</p>
</blockquote>
<p>Note that the &quot;normal&quot; qualifier effectively ties the chosen c back to the image receiver format. Kodak freely applies this
approach to formats ranging from 35 mm to 8x10 inches, so why not take it into
the digital realm?</p>
<h5>Technical Note: The <i>Ilford Manual of Photography</i>,<i> </i>the British
analog to the <i>Kodak Professional Photoguide</i>, propounds a slightly
different 1/1000 rule based on the true focal length of the lens at hand, not
necessarily the normal lens. This yields an elegant result: h = 1000 * d = 1000
* f / N, where d is the physical diameter of the aperture. As attractive as that
is, I'm sticking with the Kodak approach for now.</h5>
<p>For 35 mm SLRs, f<sub>normal</sub> is commonly taken to be 50 mm. Assuming
that f<sub>normal</sub> for a CCD is just 50 mm / FLR<sub>35</sub>, then for my
camera's 2.11MP Sony CCD with effective diagonal D = 8.0 mm,</p>
<ul>
  <li>
    <p style="margin-bottom: 9">f<sub>normal</sub> = 9.3 mm = 1.43x zoom</li>
  <li>c = f<sub>normal</sub> / 1000 = 0.0093 mm = D/860</li>
</ul>
<p>This is the circle of confusion underlying the <a href="#hyperfocal_table">hyperfocal
table above</a>. It's a little over <a href="#twice"> twice the CCD's sensel
size</a> (0.0039 mm), but it
nicely fits the manual focus DOF charts published in the manual for my old
C-2000Z, which uses the exact same lens and CCD as my C-2020Z. (The C-2020Z
manual has no DOF charts for some reason.) To the extent that Oly determined these charts empirically, they lend support
to this 0.0093 mm circle estimate for the 2.11MP Sony CCD and any camera that
uses it.</p>
<h4><a name="twice"></a>The &quot;twice sensel size&quot; Approach</h4>
<p>Some propose twice sensel size as a reasonable guess for c in any digital
camera on the assumption that the manufacturer has matched <a href="#resolving">lens
resolution</a> to CCD geometry in an optically <i>and</i> economically sound
way. <a href="#g1_circle">Canon's G1 pan-focus circle</a> of 0.0071 mm = D/1239
is very close to twice the sensel size of 0.00345 mm. The 0.0093 mm = D/860
circle I've tentatively adopted for cameras using the once ubiquitous original 2.11MP Sony CCD is
19% greater than twice sensel size (0.0078 mm), while the 0.0063 mm = D/1280 CoC
derived by <a href="#backward">working backward</a> from a 10x7.5&quot; print is
19% smaller. Note the
substantial difference in these circles when expressed as a fraction of
diagonal.&nbsp;</p>
<p>Note that this is the only approach I'll discuss that takes into account the
discrete nature of a digital image receiver, and it does so only via sensel
size. At constant sensor diagonal and aspect ratio, it is inversely proportional
to the horizontal effective sensel count.</p>
<h4><a name="g1_circle"></a>Data Point: The Canon G1 Pan-Focus Circle for Sony's
1/1.8&quot; 3.3MP CCD</h4>
<p>A valuable manufacturer-based digital circle of confusion data point comes from the Canon
PowerShot G1, which by all accounts uses the same Sony 1/1.8&quot; 3.3MP CCD found in
Oly C-30x0Z cameras. Since the G1's &quot;pan-focus&quot; mode is nothing more than a
built-in <a href="#hyperfocal">hyperfocal technique</a>, its factory-programmed
settings can be used to divine Canon's idea of a proper circle for its CCD.</p>
<p>Fini Jastrow of Hamburg, Germany kindly wrote:</p>
<blockquote>
  <p>The Canon G1 comes with a special 'pan-focus' mode using
  [hyperfocal technique]. It fixes the focal length to 7 mm, the aperture on
  f/5.6 and sets the focal distance to 1.24 m. This info is taken from the EXIF
  data. The manual of the camera confirms 7 mm, f/5.6 and specifies a 'nearest
  focus' of 0.65 m. That seems quite consistent.</p>
  <p>So calculating the circle c form this manufacturer gives
  values results to c = ( f * f ) / ( N * h ) = 0.0071 mm....</p>
  <p>So the manufacturer's circle is 2 times the size of one
  sensel. [Sony quotes a sensel pitch of 0.00345 mm for this CCD.] I'd say what
  they use should be a conservative number so they're on the safe side. My guess
  is that you do not lose that much information due to color interpolation...</p>
</blockquote>
<p>To my mind, Fini's analysis establishes 0.0071 mm = D/1239 as the circle to
beat for the many cameras using the same 1/1.8&quot; 3.3MP CCD. But does it also
apply to other 1/1.8&quot; CCDs with higher sensel counts?
I'm not prepared to say at this point, but my gut favors the <a href="#twice">twice
sensel size</a> approach over circles determined solely by CCD diagonal. &nbsp;</p>
<hr>
<h3><a name="confusion"></a>Confusion Is the Operative Word</h3>
<p>Circles of confusion generate all kinds of confusion on the digital side. To
my mind, the central question remains: Do conventional film-based approaches to
circle choice <i>really</i> apply to an electronic image receiver like a CCD
with discrete sensels coupled to an internal anti-aliasing filter, a Bayer pattern color
interpolation scheme and a sharpening algorithm applied (sooner or later) to
recover detail lost to the anti-aliasing filter? None of these digital
complications have direct analogues on the film side. Since I have yet to see a
convincing treatment of their bearing on digital c values, I'm not prepared
to ignore them; nor am I knowledgeable enough to deal with them head-on.</p>

<h4>Film-Based Circles</h4>

<p>Not that there's any real consensus on how to choose a circle of confusion
(c) on the film side. Film photographers variably calculate c as a fraction of D, the
frame diagonal of the film format at hand, or from one or another <a href="#kodak">f/1000 rule</a>
with widely varying
results. The 0.03 mm circle most commonly used in DOF calculations for 35 mm
photography corresponds to D/1440, but some favor the more stringent 0.025 mm = D/1730
criterion championed by Zeiss, at least for more demanding viewing situations.
Assuming the eye to be capable of at most 2 arc minutes of angular resolution
on a print, as is commonly done, the D/1730 circle guarantees acceptable
sharpness in a 10-inch print of a 35 mm negative at viewing distances as close
as 12 inches, while the D/1440 circle pushes you back to 14 inches.</p>

<div align="left">
  <table border="2">
    <tr>
      <td valign="bottom" colspan="5">
        <h4>Circles of Confusion (mm) Potentially Applicable to Digitals</h4>
      </td>
    </tr>
    <tr>
      <td valign="bottom"><b>Format</b></td>
      <td valign="bottom"><b>35 mm film&nbsp;</b></td>
      <td valign="bottom"><b>5.2MP CCD&nbsp;</b></td>
      <td valign="bottom"><b>3.3MP CCD&nbsp;</b></td>
      <td valign="bottom"><b>2.1MP CCD&nbsp;</b></td>
    </tr>
    <tr>
      <td>Type (in)</td>
      <td align="right">n/a</td>
      <td align="right">1/1.8</td>
      <td align="right">1/1.8</td>
      <td align="right">1/2</td>
    </tr>
    <tr>
      <td>Diagonal D (mm)</td>
      <td align="right">43.3</td>
      <td align="right">8.94</td>
      <td align="right">8.94</td>
      <td align="right">8.00</td>
    </tr>
    <tr>
      <td>f<sub>normal</sub> (mm)</td>
      <td align="right">50</td>
      <td align="right">10.1</td>
      <td align="right">10.1</td>
      <td align="right">9.3</td>
    </tr>
    <tr>
      <td><a href="#flr35">FLR<sub>35</sub></a></td>
      <td align="right">1.000</td>
      <td align="right">4.923</td>
      <td align="right">4.923</td>
      <td align="right">5.385</td>
    </tr>
    <tr>
      <td><a href="#twice">Twice sensel size</a></td>
      <td align="right">n/a</td>
      <td align="right">0.0056</td>
      <td align="right">0.0069</td>
      <td align="right">0.0078</td>
    </tr>
    <tr>
      <td><a href="#backward">End-use (D/1280)</a></td>
      <td align="right">0.034</td>
      <td align="right">0.0071</td>
      <td align="right">0.0071</td>
      <td align="right">0.0063</td>
    </tr>
    <tr>
      <td><a href="#g1_circle">G1 pan-focus mode</a></td>
      <td align="right">n/a</td>
      <td align="right">n/a</td>
      <td align="right">0.0071</td>
      <td align="right">n/a</td>
    </tr>
    <tr>
      <td><a href="#kodak">f<sub>normal</sub> / 1000</a>&nbsp;</td>
      <td align="right">0.050</td>
      <td align="right">0.0101</td>
      <td align="right">0.0101</td>
      <td align="right">0.0093</td>
    </tr>
    <tr>
      <td>D/1440</td>
      <td align="right">0.030</td>
      <td align="right">0.0061</td>
      <td align="right">0.0061</td>
      <td align="right">0.0056</td>
    </tr>
    <tr>
      <td>D/1730</td>
      <td align="right">0.025</td>
      <td align="right">0.0051</td>
      <td align="right">0.0051</td>
      <td align="right">0.0046</td>
    </tr>
  </table>
</div>
<p>On the digital side, the <a href="#twice"> twice CCD sensel size</a>, D/1440 and D/1730 circles all allow
viewing of a 10-inch print made with either CCD from at worst a very reasonable
distance of 19-20 inches. The <a href="#backward">end-use approach</a>
incorporates a larger print circle that allows viewing from 17 inches. Errors due to pixellation in consumer-grade CCDs typically fall within
even the D/1730 circle, as they do for all of the CCDs shown here, but
that doesn't take into account the smearing of scene information that goes on
with internal anti-aliasing filters, Bayer pattern color interpolation and image
sharpening. These influences would tend to increase effective circle size.</p>

<p> DOF graphs published in the Oly C-2000Z manual suggest an
effective circle of confusion nearly twice the D/1440 circle.&nbsp; My DOF guru Andrzej Wrotniak finds that the
D/1440 circle works well enough for his C-3030Z, but it's ~14% smaller than the D/1239 circle Canon
figured for
pan-focus (hyperfocal) mode for the same 3.3MP sensor. Note also that all the <a href="#kodak">f<sub>normal</sub> / 1000</a> 
and diagonal-based circles are identical for the 3.3MP and 5.2MP sensors.
Doesn't the smaller sensel size count?</p>

<p><a name="reservations"></a>That kind of scatter leads me away from any
circle approach based solely on CCD diagonal. I'm equally leery of approaches
based on focal length because they also ultimately tie back to the frame
diagonal. The <a href="#kodak">f<sub>normal</sub> / 1000</a> approach happens to
yield a reasonable result for my 2.1MP camera but doesn't jibe with the circle
Canon uses for the G1's pan-focus feature.</p>

<p>But wait! The common 35 mm film circles in the last 3 rows of the table
above are all over the map for 35 mm film as well! Could it be that circle
choices don't matter that much after all? Film photography is a mature
technology with many knowledgeable and exacting practitioners. If one of these
film-based circle approaches were a clear winner for 35 mm film, you'd think
practice would have settled on it by now.</p>

<h4><a name="empirical"></a>In the End, c is Empirical&nbsp;</h4>
<p>Ultimately, the correct choice of c is an empirical matter intimately tied
to the intended end-use of the image. The &quot;correct&quot; circle is the one
that yields an acceptably sharp image (say, a print of a certain size viewed
from a certain distance) when used to guide manual focusing in the field, as in <a href="#hyperfocal">hyperfocal
technique</a> guided by a hyperfocal distance table calculated from that circle.
If the near and far limits of DOF end up acceptably sharp when you focus at the
calculated distance and view the final image in the required manner, then the
circle worked. If the distant horizon comes out blurry, then it didn't.</p>
<p>If you really need a reliable circle for your camera, and you have a sufficiently accurate
manual
focus interface, then
your best bet would be to pick a series of candidate circles based on the
considerations above, test them all against your most important end-uses, and
narrow it from there, as detailed <a href="#hyperfocal_custom">above</a>.&nbsp;</p>
<p>Acknowledgement: Many thanks to <a href="http://www.wrotniak.net">
Andrzej Wrotniak</a> and&nbsp; Fini Jastrow for their technical help here.</p>

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<hr>

<h2><a name="motion"></a><b>Motion Management</b></h2>
<p>Motion happens. Image-stabilized cameras can sense and to some
extent compensate for camera motion, but no consumer-grade still camera I know
of can deal with motion occurring within the scene. So it's still largely up to
the photographer to manage motion's tendency to blur the image in a proactive
manner. A
little blur may impart a beneficial show of movement in an image with a mountain
stream, but most of the time, motion artifacts are to be eliminated.&nbsp;</p>
<p>Motion happens on both sides of the lens.&nbsp;</p>
<ul>
  <li>
    <p style="margin-bottom: 9">If <a href="#shake">camera motion</a> is the problem,
    rock-stable support and remote triggering are the ultimate cures when
    feasible, but you may well be forced to shorten exposure times when shots
    must be handheld. (Electronic image stabilization can be very helpful with
    handheld shots, but few current digital cameras offer it.)&nbsp;</li>
  <li>If the subject's doing the moving and you need to <a href="#stop-action">stop
    the action</a>, suitably short exposures are your best defense against
    unwanted blur.</li>
</ul>
<p>Let's look at each type of motion separately.</p>
<hr>
<h3><b><a name="shake"></a>Camera motion</b></h3>
<p>Your efforts to minimize <a href="#noise"> noise</a> and optimize <a href="#dof"> DOF</a> and
<a href="#resolving">resolving power</a> will come
to naught if your images are blurred by <i> camera shake</i>�the camera motion
that accompanies the act of taking an exposure.</p>
<p>In handheld shots, the main source of camera shake is the
wetware�the photographer. Human photographers can only hold so still for so
long, and can only release the shutter so gingerly. Good technique and practice
can improve steadiness on both counts, but there will almost always be an available
shutter speed too slow for handholding.</p>
<p><a name="support"></a>When handholding proves infeasible, an solid <b>camera support</b> is in
order. Supports come in many forms�tripods, <a href="c-2000z/monopod/index.htm">monopods</a>,
bean bags, nearby rocks and logs�each with pros and cons. But even with a
solid tripod, a heavy finger on the shutter release can result in visible camera
shake, and that's where remote triggering comes in. Some higher-end digital and
film cameras now come with IR remote controls ideal for eliminating this last
vestige of shake.</p>
<p>In 35 mm SLRs, vibrations generated when the viewfinder mirror flips up out
of the way can also cause visible camera shake, even with a sturdy tripod <i>and</i>
remote triggering. Fortunately, most digital cameras lack internal moving parts
with such momentum.</p>
<hr>
<h3><b><a name="steadiness"></a>Steadiness</b></h3>
<p>When steadiness counts and you're the only camera support around,</p>
<ul>
  <li>
    <p style="margin-bottom: 9">Use
shutter priority or manual mode to work out a speed you can handhold reliably. You'll likely
end up with enough <a href="#dof">DOF</a>, even at the widest apertures.</li>
  <li>Frame
your shots with the LCD if necessary, but shoot with the viewfinder with the camera
held firmly against your brow to further reduce camera shake.</li>
</ul>
<p><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;Keep in mind that longer focal lengths literally magnify camera shake.&nbsp;</p>

<h4><a name="1/f35"></a> The 1/f<sub>35 </sub>Rule</h4>

<p> To
improve sharpness in handheld shots,&nbsp;</p>

<table border="0">
    <tr>
        <td valign="top"><a href="index.htm#warranty"><em><strong><img src="tumbling_arrow.gif" alt="Marks the gotchas" align="left" border="0" hspace="0" width="16" height="16"></strong></em></a></td>
        <td valign="top"><b>Plan to use shutter speeds faster than 1/f<sub>35</sub>,
where f<sub>35</sub> is your final 35 mm equivalent focal length after zooming and
          any
converter lenses you might have mounted.</b></td>
    </tr>
</table>

<p>For example, at 105 mm (full zoom on my C-20x0Zs),
keep shutter speeds faster than 1/105 sec. See the <a href="#stop">stop-action section</a>
 below for tips on getting the fastest possible shutter speeds.</p>
<h4>Know Your Limits</h4>

<p>Get
a feel for your own handholding ability�before it counts. With a digital
camera, learning your own handholding limits will take only a few minutes of your time.</p>

<p>The 1/f<sub>35 </sub>rule of thumb works for most
35 mm photographers, but since weight dampens shake and digital cameras weigh
considerably less than most 35 mm SLRs, it may be wise to work on the conservative side of
the rule. Your own handholding limits may
differ considerably in any event, depending on age, caffeine load, proximity to tax time,
etc.</p>

<h4>Bracket for Shake, Too</h4>

<p><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;<a href="#bracketing">Bracketing</a>
for camera shake is a very effective strategy, at least on the digital side. By
taking several duplicate exposures, I often come away with at least one
acceptably steady shot, even at very marginal handholding shutter speeds. If for
no other reason, the practice at holding a particular shot steady seems to pay.
I find bracketing for shake particularly useful in my <a href="ir.htm">infrared</a>
and <a href="c-2000z/monopod/index.htm">monopod</a> shots.&nbsp;</p>

<hr>

<h3><a name="stop-action"></a><b>Stop-Action</b></h3>
<p>How fast a shutter is fast enough to stop motion? That depends on the
subject's speed and direction and the final magnification of your lens. Here's a
handy ballpark formula modified for digital camera use:</p>
<blockquote>
<p><b>Stop-action time (sec) ~ (distance * direction) / (20 * f<sub>35</sub> * speed)</b></p>
</blockquote>
<p>where the subject's <i>speed</i> is in miles per hour, <i>distance</i> to the
subject is in feet, the subject's <i>direction</i> is</p>
<ul>
  <li>
    <p style="margin-bottom: 9">1 for motion across the field of view (FOV)</li>
  <li>
    <p style="margin-bottom: 9">2 for motion at 45� to the camera-subject line</li>
  <li>4 for motion directly toward or away from the camera</li>
</ul>
<p>and <i>f<sub>35</sub></i> is the 35 mm equivalent focal length (EFL).&nbsp;</p>
<p>If you can't get a fast enough shutter speed at ISO 100, you may need to bump
<a href="#iso">ISO</a>  and pay the price in <a href="#noise"> image noise</a>. This is the one
instance I can think of where my C-2020Z's <a href="#auto-iso"> auto-ISO</a> feature
makes some sense, particularly when the desired action is hard to see coming.&nbsp;For
a price, large-sensor digital cameras like the Nikon D1x and the Canon D30 and
D60 are very well suited to stop-action work in limited light. They make faster
shutter speeds feasible by delivering very acceptable <a href="#noise">noise</a>
levels at <a href="#iso">ISO</a> 400 and beyond.</p>
<p>When you're
really pushing shutter speed to the limit in shutter-priority or manual metering
mode,
make sure the camera can follow you there with a reality
check of the exposure display usually found on your camera's rear LCD. It may
well save you from an underexposed mess, as
explained <a href="#monitoring">above</a>.</p>
<p>For subjects within flash range in limited ambient light, flash can often
freeze motion more effectively than a fast shutter. If ambient light is high
enough, a <a href="c-2000z/low-light/index.htm#slow">slow shutter flash sync</a>
technique may be appropriate.</p>

<h4><a name="panning"></a>Panning</h4>

<p>Following a moving subject with the camera to freeze its motion against a
blurred background is an important action technique known as <i>panning</i>. The
background blur heightens the sense of subject motion. In limiting light,
panning may be your only option with extremely fast-moving subjects like
racecars at speed. I won't go into detail on panning techniques, but I will
offer these pearls:</p>

<ul>
  <li>
    <p style="margin-bottom: 9">Continue the panning motion well after
    completion of the exposure, like the follow-through in a golf swing.</li>
  <li>
    <p style="margin-bottom: 9">Practice, practice, practice.</li>
</ul>
<p>Handheld panning is challenging but workable with practice. A tripod with a
panning head reduces the number of degrees of freedom you have to control at
exposure time.</p>

<h4><a name="timing"></a>Timing</h4>

<p>Freezing the action is one thing. Catching the right moment is another. In
action photography, anticipation is a requisite skill requiring considerable
practice. The required rhythm varies from event to event. With a digital camera,
on-the-scene practice and feedback are very helpful. In limited light, <a href="#auto-iso">auto-ISO</a>
can free you up to concentrate on your timing, but use it very carefully.</p>

<p>As with any auto-focus, auto-exposure camera, the time between pressing the
shutter release and exposure can be unexpectedly long and variable on digital
cameras, but these potentially fatal delays and uncertainties can be reduced to
manageable levels, at least with most higher-end digital cameras. Learn to deal
with your camera's <a href="c-2000z/tips/index.htm#timing">timing issues</a>
beforehand.</p>

<p>For an excellent illustrated discussion of digital action photography
stressing timing and the importance of minimizing <a href="c-2000z/tips/index.htm#lag">shutter
lag</a>, be sure to visit Kevin Bj�rke's Canon G1-oriented <a href="http://www.botzilla.com/photo/G1speed.html">Shooting
Action with the PowerShot</a>. It's well worth a read for any digital
photographer.&nbsp;</p>

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<hr>

<h2><b><a name="dynamic"></a>Dynamic Range</b></h2>
<p>High-contrast scenes can easily exceed your camera's <i>effective dynamic range</i>�the
range of light intensities your CCD can record without complete loss of detail in
either the
highlights or the shadows.&nbsp;</p>
<p>Technical Note: There are many possible definitions of dynamic
range, some quite technical and some applicable only to the CCD itself. Here, I'm sticking to the effective dynamic range
experienced by the photographer in the field. In <a href="#zone">zone system</a>
parlance based on a 0-10 scale, it's the number of stops of metered light
intensity separating the bottom of Zone 2 from the top of Zone 8 in a single
high-contrast scene.&nbsp;&nbsp;</p>
<p> I've seen effective dynamic range (DR) estimates of 2-8 <a href="#stops">stops</a>
for digital camera. Photographically speaking, that ranges from dismal to
excellent, respectively, but even 8 stops pales before the truly phenomenal effective dynamic range of the human <a href="vision.htm#brain-eye">brain-eye
system</a>, which can accurately record
detail in single scenes with light intensities ranging over a factor of ~30,000 or ~15 <a href="#stops">stops</a>.</p>
<hr>
<h3> <a name="excess_contrast"></a>Excess Contrast</h3>
<p> Light intensities in natural scenes can exceed a factor of 2,000 or 11 <a href="#stops">stops</a>. <a href="vision.htm">Human vision</a> can easily handle such spreads,
but good color slide film can barely capture an intensity factor of
32, or 5 stops. Some digital cameras and B&amp;W films approach 8 stops.</p>
<p> Little surprise, then, that DR issues underlie many
a large discrepancy between what the brain-eye sees and the camera records. DR mismatches are all too common in photographic practice, particularly on
bright sunny days, when the highlights are very bright and the shadows very
deep.&nbsp;</p>
<p> The gap between real and recordable contrast levels amounts to <i>excess
contrast</i>. The task of managing excess contrast falls to the photographer.
Ignoring it is a sure recipe for burned-out highlights,
black-hole shadows, or both.</p>
<hr>
<h3><b><a name="tough"></a>Tough Choices</b>&nbsp;</h3>
<p>In the face of <a href="#excess_contrast">excess contrast</a>, you may find detail sacrifices
impossible to avoid, even with the best of technique. But one thing's certain�letting the camera decide what to do about
excess contrast is very
risky. If you decide what detail to preserve
and what to let go and take steps to effect those choices, you have a much better
chance of approximating with the camera's effective DR what the brain-eye sees.</p>
<p>Reliable rules are hard to come by here, but generally speaking, with digital
cameras,</p>
<blockquote>
  <p><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a><b>&nbsp;Even out
  the lighting as best you can�e.g., by selectively suppressing highlights
  with a <a href="#filters">filter</a> or by using <a href="#fill">fill flash</a>
  or <a href="#reflectors">reflectors</a>.</b></p>
  <p><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a><b>&nbsp;Expose to
  preserve detail in the remaining highlights as best you can.</b></p>
  <p><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a><b>&nbsp;Bring up
  the shadows using <a href="#fill">fill flash</a>, <a href="#reflectors">reflectors</a>
  or in post-processing using tone curves as needed.</b></p>
</blockquote>
<p>This approach may well exacerbate visible noise in the
shadows�and, of course, nothing can be done about completely black
shadows�but noisy shadows are usually much less obtrusive than the alternative
white-outs, which have no cure.</p>
<p>This thoroughly digital <a href="#excess_contrast">excess contrast</a> strategy runs counter to the
film-based <a href="#zone">zone system</a> maxim, &quot;Expose for the shadows
and develop for the highlights&quot;, as discussed <a href="#zone_upsidedown">below</a>,
primarily because CCDs saturate much less gracefully than most films
do. For one thing, <a href="#bloomng">blooming</a> of saturated CCD
photosites (sensels) into adjacent ones only makes white-outs more obvious. To minimize blooming, most modern
CCDs drain off &quot;excess&quot; photoelectrons before they can spill over
(bloom) into adjacent photosites, but these drains effectively clip the signal at
the high end.</p>
<hr>
<h3><a name="bloomng"></a>Blooming</h3>
<p>No discussion of excess contrast in digital photography would be complete
without an explanation of the digital artifact known as <i>blooming</i> well
illustrated <a href="c-2000z/low-light/index.htm#blooming">here</a>. If you
reserve the term &quot;noise&quot; for unwanted time-dependent random signal
variations, as most engineers do, blooming isn't really noise, but it's a fatal
image flaw nevertheless, with no generally satisfactory post-processing cure.</p>
<p>Each sensel (photosite) in a CCD is like a bucket. Incoming photons knock
electrons from the chip substrate into the bucket, at which point the electrons
become &quot;photoelectrons&quot;. When the CCD reads off the image, it simply
measures the free charge�counts the photoelectrons�in each bucket. However,
when overexposure overfills a bucket, excess photoelectrons spill over into
adjacent buckets, which then register artifactually increased photoelectron
counts. That's how blown-out highlights spread or &quot;bloom&quot; into
adjacent image areas.</p>
<p>Modern CCDs run gutters between the buckets to drain off excess
photoelectrons, but the gutters aren't always effective, so you still have to
manage digital exposures actively to avoid blooming in predisposing
situations.</p>
<p>Blooming is aggravated by long exposures and by physically small sensels,
which overflow sooner than larger ones.</p>
<p>Since in-camera meters often average their readings over areas considerably
larger than the highlights subject to blooming, you can't trust your meter to
avoid blooming. <a href="#ec">Exposure compensation</a> (EC) is a handy way to
override the meter to keep blooming at bay. If you're not sure how much negative
EC to dial in, <a href="#bracketing">bracket</a> like crazy. With a digital
camera, it's free, and eventually you'll get a feel for it.&nbsp;</p>
<p>Speaking of free, it's all too easy to generate blooming and play around with
it. Just set your camera for auto exposure and <a href="moon.htm">shoot the full
moon</a> in a dark sky or a bright lamp in a dark room.</p>
<h4><b>Do UV and IR Contamination Contribute to Blooming?</b></h4>
<p>Some believe that UV and <a href="ir.htm#contamination">IR contamination</a>
contribute to blooming in visible light digital photographs near overexposure.
IR-induced blooming sounds like a plausible explanation when my IR-sensitive Oly
C-2020Z blows out certain red flowers in bright sunlight, but an IR cut filter
doesn't correct the problem. In conjunction with high-order lens aberration, UV-induced blooming
might conceivably play a role in the
&quot;purple fringing&quot; artifact seen in certain unusually UV-sensitive
cameras like the Canon PowerShot G1 and Canon IS Pro90 shooting close to
overexposure, but I remain unconvinced.</p>
<hr>
<h3><b><a name="blending"></a>Advanced Post-Processing for Excess Contrast</b></h3>
<p>Fortunately, digital imaging offers effective post-processing solutions to
the <a href="#excess_contrast">excess contrast</a> problem, including</p>
<ul>
  <li>
    <p style="margin-bottom: 9">image blending</li>
  <li>
    <p style="margin-bottom: 9">contrast masking</li>
  <li>
    <p style="margin-bottom: 9">channel mixing</li>
</ul>
<h4>Image Blending</h4>
<p>If all else fails, you can take 2 otherwise identical exposures of your high-contrast
scene 2 or more stops apart and <i>blend</i> them in post-processing. One exposure preserves the shadow detail and the other the highlight detail
you're after. A tripod and remote triggering are required to insure exact image registration. Max Lyons' <a href="http://cgibin.rcn.com/maxlyons/cgi-bin/image.pl?gallery=1&amp;showThumbnails=1">blended
images</a> beautifully illustrate the striking results blending can achieve.</p>
<p>Michael
Reichmann's superb <a href="http://www.luminous-landscape.com/tutorials/blended_exposures.shtml"> blending tutorial</a>
details the blending process in
PhotoShop 5.5. (If you're starting with properly aligned digital camera images, skip
over the scanning and aligning steps 1-11.)</p>
<p>Peter
iNova's PhotoShop <a href="http://www.digitalsecrets.net/secrets/DynamicRanger.html">blending tutorial</a> takes another effective approach
that doesn't involve Reichmann's complex selections but still requires precise
registration of redundant images�in this case, 3 images exposed at -2, 0 and +2 <a href="#ec">EC</a>
 settings. I find iNova's tack more appealing for routine use.</p>
<p>Finally, <a href="http://www.fredmiranda.com/article_2/index.html">Fred
Miranda's linear gradient approach</a> mimics the effect of a graduated neutral
density filter.</p>
<h4>Contrast Masking and Channel Mixing</h4>
<p>Other Reichmann tutorials pertinent
to <a href="#excess_contrast">excess contrast</a> control in post-processing include
<a href="http://www.luminous-landscape.com/tutorials/contrast_masking.shtml">contrast
masking</a> and <a href="http://www.luminous-landscape.com/b&amp;w_better.htm">channel
mixing</a>, the latter for <a href="bandw.htm"> B&amp;W images</a>.&nbsp;These
techniques are generally less effective than image blending but don't require
multiple perfectly registered exposures. If you forgot your tripod, give these a
whirl.</p>
<hr>
<h3><b><a name="spot"></a>Spot Metering</b></h3>
<p><i>Spot metering</i>  narrows in-camera metering to a small central region marked in
the viewfinder. It allows selective metering of high-priority elements in your
scene to insure proper exposure. With spot metering enabled, my C-2020Z
meters a 3-9� solid angle, depending on zoom setting.&nbsp;</p>
<p>To take full advantage of spot metering,</p>
<ul>
  <li>
    <p style="margin-bottom: 9">Spot-meter carefully on the main subject and on
    the highlights and shadows containing detail to be preserved. Use your spot
    meter to probe high-contrast scenes for the <a href="#excess_contrast">excess
    contrast</a> confronting you.</li>
  <li>
    <p style="margin-bottom: 9">Make a note of the apertures and shutter speeds reported by the camera.*</li>
  <li>
    <p style="margin-bottom: 9">Understanding that the respective metered exposures will render each of
    the targets in a medium tone, juggle the final exposure to reach a
    prioritized best-fit solution for subject, highlight and shadow <a href="#tonality">tonalities</a>
    according to your camera's tone vs. exposure behavior.</li>
  <li>Use manual exposure mode, or <a href="#ec">exposure compensation</a> in a
    priority mode, to reach the desired exposure by way of <a href="#reciprocity">reciprocity</a>.</li>
</ul>
<p>* Warning: Since a half-press of the shutter release
locks both exposure and auto-focus in program and priority modes on many digital
cameras,
&quot;dragging&quot; an exposure reading from one part of the frame to another
may jeopardize focus when the areas involved aren't the same distance from the
camera.</p>
<p>Of course, all this is easier said than done, and it wasn't all that easy to say.</p>
<h4>Narrowing the Spot with Zoom</h4>
<p>
If you can't spot-meter selectively on a small subject at wide angle, try
zooming in on it first. On my C-2020Z, spot meter coverage narrows from ~9� to
~3� as I zoom from full wide angle (1x, 35 mm) to full zoom (3x, 105 mm). Once
the reading's in hand, zoom back out for the shot.</p>
<hr>
<h3><a name="fill"></a><b>Fill Flash</b></h3>

<p>A dark backlit subject against a bright background is a common photographic
challenge. With averaged or matrix metering, you're likely to underexpose your
subject, possibly with severe loss of detail. Spot-metering the subject alone
will help you expose the subject properly, but background detail may suffer
greatly in the process.</p>

<p>If you can't rearrange the lighting but you're within flash
range, you can narrow the scene's dynamic range by forcing on your flash to add light to the subject. This technique is known as <i>fill flash</i>,
and it's a role your camera's otherwise rather limited onboard flash plays
fairly well. Many current cameras like the C-2020Z provide fill flash automatically when auto-flash is enabled.</p>

<p>Unfortunately, fill flash has its disadvantages:</p>

<ul>
  <li>
    <p style="margin-bottom: 9">The color temperature (character) of flash light often differs greatly
    from the ambient sunlight or incandescent (tungsten) light dominating your
    scene. Skin can take on a ghoulish cast in the bluer light of the flash,
    particularly with an
    incandescent <a href="#wb">white balance</a> setting.</li>
  <li>Unnatural &quot;spot-light&quot; illumination patterns and harsh shadows
    are all too common.</li>
</ul>
<p>Luckily, these shortcomings can often be avoided entirely or substantially diluted
with...&nbsp;</p>

<hr>

<h3><b><a name="reflectors"></a>Ambient Light Reflectors</b></h3>

<p align="left">One or more strategically located diffuse reflectors can pump <i>ambient
light</i> into your shadows in a natural-looking way without disturbing the
dominant color temperature of the scene. The more diffuse the
reflected light, the less shadowing and spot-light effect you'll get. Reflectors can be used in lieu of or in conjunction with <a href="#fill">fill
flash</a>.&nbsp;</p>

<p align="left">There are many reflector designs on the market (see, for
example, <a href="http://www.cameraworld.com">www.cameraworld.com</a> or <a href="http://www.bhphoto.com">www.bhphoto.com</a>).
White poster board works well, but it's awkward to carry. (I'm experimenting with
a compact crinkly Mylar &quot;emergency blanket&quot; that folds up to fit in my
medium-sized camera bag, but proper support is an on-going challenge.) With
reflectors, a patient
and willing human accomplice can be very helpful.</p>

<hr>
<h3><b><a name="filters"></a>Filtering
Excess Contrast Selectively</b></h3>
<p> <a href="filters.htm#gnd">Graduated
neutral density filters</a> and <a href="filters.htm#polarizers">polarizers</a>&nbsp;
can reduce <a href="#excess_contrast">excess contrast</a> by selectively filtering highlights under certain
circumstances discussed at their respective links.</p>
<p>Filters can be used in combination with <a href="#spot">spot metering</a>, <a href="#fill">fill flash</a> 
and <a href="#reflectors">reflectors</a> to
help you manage excess contrast. In combination, knocking down highlights and filling in shadows
become even more effective at reducing the scene's contrast�hopefully to a level
the camera can handle.&nbsp;</p>

<hr>
<h3><a name="dr_test"></a><b>Testing Your Camera for Effective DR</b></h3>

<p>To my <a href="#test2">testing</a>, my Oly C-2020Z has an effective DR of
~7 <a href="#stops">stops</a>. This result jives with the 1 stop per zone effective C-2020Z DR implied in an
August, 2000 digitalFOTO magazine article on the application of <a href="#zone">zone
system techniques</a> to B&amp;W work on that camera.</p>

<p>Using a different test method documented <a href="http://tawba.tripod.com/dynrange.htm">here</a>,
Max Lyons came up with ~8 stops for his Nikon CoolPix 990. <a href="http://www.digitalsecrets.net/secrets/DynamicRanger.html">Peter
iNova's image blending tutorial</a>  quotes an 8.8-stop dynamic range for Nikon
compact digital cameras like the CoolPix 990, but he doesn't reveal how he
arrived at that number.</p>

<p>These digital DR results compare favorably with the generous DR of good
B&amp;W film. I no longer consider them a spurious reflection of the 8-bit analog-to-digital
conversion these cameras perform on their CCD outputs. The oft-repeated claims
that digital cameras have &quot;limited&quot; effective DRs clearly don't apply
across the board.&nbsp;</p>

<p> Based on a 7-stop DR, I now work off a 1 stop per zone tonality chart
similar to the <a href="#tone_table">sample
chart below</a>, so far without a hitch.</p>

<h4><a name="test2"></a>Measuring Your Own Effective DR</h4>

<p> If you plan to pursue <a href="#tonality"> tonal control</a> with or without
the <a href="#zone">zone system</a>, you'll need to make
your own <a href="#tone_table">tone-versus-exposure table</a>. With a digital camera, the required
calibration has never been easier.</p>

<p>I cobbled together my own direct single-image <i>effective DR</i> test using a
highly sophisticated textured high-contrast target�a
white corrugated cardboard box containing a dark green terry cloth towel. I
turned one side of the box squarely toward the February afternoon sun so as to
place the
towel inside the box in deep shadow. I shot the entire target in a single frame
like so:&nbsp;</p>

<ul>
  <li>
    <p style="margin-bottom: 9">monopod support</li>
  <li>
    <p style="margin-bottom: 9">ISO 100</li>
  <li>
    <p style="margin-bottom: 9">manual exposure with fixed
aperture at f/8</li>
  <li>
    <p style="margin-bottom: 9">auto white balance</li>
  <li>
    <p style="margin-bottom: 9">in-camera sharpening and flash disabled&nbsp;</li>
</ul>
<p> Careful spot-metering at full zoom
confirmed a reproducible spread of 7 full stops between the deepest shadow on
the towel and
the sunward side of the box. (I probably could have widened the gap by
performing the test at high noon during the summer with a black towel, but the
spread obtained proved adequate for this test.)</p>

<p>In a single image exposed at f/8 @ 1/100, the highlights and shadows barely retained recognizable detail
confirmed with histogram analysis. In <a href="#zone">zone system</a> terms,
they fell at the top of Zone 8 and the bottom of Zone 2, respectively:</p>

<table border="2">
  <tr>
    <td colspan="2" valign="top" align="left">
      <p><b>DR Test 2�Towel in Box in Direct Afternoon
      Sun</b></p>
    </td>
  </tr>
  <tr>
    <td valign="top" align="left">
      <p><b>Zone 8&nbsp;</b></p>
    </td>
    <td valign="top" align="left">
      <p>Last vestige of box detail before white-out (metered at f/8 @ 1/6, or
      EV = 8.6)</p>
    </td>
  </tr>
  <tr>
    <td valign="top" align="left">
      <p><b>Difference&nbsp;</b></p>
    </td>
    <td valign="top" align="left">
      <p>7 stops over 7 zones (bottom of 2 to top of 8) =&gt; 1 stop per
      zone</p>
    </td>
  </tr>
  <tr>
    <td valign="top" align="left">
      <p><b>Zone 2&nbsp;</b></p>
    </td>
    <td valign="top" align="left">
      <p>Last vestige of towel detail before black-out (metered at f/8 @ 1/800,
      or EV = 15.6)&nbsp;</p>
    </td>
  </tr>
</table>

<p>I'm now satisfied that the C-2020Z runs very close to 1 stop per zone.&nbsp;</p>

<h5>* Technical Note: I first attempted to measure my Oly C-2020Z's effective
dynamic range (DR) using a medium gray terry cloth towel as a finely detailed
target, with fixed ISO 100, fixed sunny white balance, manual exposure, tripod,
IR remote triggering and flash disabled. Here's what I found:</h5>
<table border="2">
  <tr>
    <td colspan="2">
      <h5><b>Highlight Test 1�Towel in Direct Afternoon
      Sun</b></h5>
    </td>
  </tr>
  <tr>
    <td valign="top" align="left">
      <h5>Zone 5 &nbsp;</h5>
    </td>
    <td valign="top" align="left">
      <h5>Spot meter wanted f/8 @ 1/320 (EV = 14.3)</h5>
    </td>
  </tr>
  <tr>
    <td valign="top" align="left">
      <h5>Zone 8-9&nbsp;&nbsp;&nbsp;</h5>
    </td>
    <td valign="top" align="left">
      <h5>Last gasp of towel detail just before white-out (shot at
      f/8 @ 1/20, or EV = 10.3)</h5>
    </td>
  </tr>
  <tr>
    <td valign="top" align="left">
      <h5>Difference&nbsp;&nbsp;&nbsp;</h5>
    </td>
    <td valign="top" align="left">
      <h5>4 stops =&gt; ~ 1 stop per zone</h5>
    </td>
  </tr>
  <tr>
    <td colspan="2" valign="top" align="left">
      <h5><b>Shadow Test 1�Towel Just After Sunset</b></h5>
    </td>
  </tr>
  <tr>
    <td valign="top" align="left">
      <h5>Zone 5&nbsp;</h5>
    </td>
    <td valign="top" align="left">
      <h5>Spot meter wanted f/4 @ 1/50 (EV = 9.6)</h5>
    </td>
  </tr>
  <tr>
    <td valign="top" align="left">
      <h5>Zone 1-2&nbsp;&nbsp;&nbsp;</h5>
    </td>
    <td valign="top" align="left">
      <h5>Last gasp of towel detail just before black-out (shot at f/4 @ 1/800,
      or EV = 13.6)&nbsp;</h5>
    </td>
  </tr>
  <tr>
    <td valign="top" align="left">
      <h5>Difference&nbsp;&nbsp;&nbsp;</h5>
    </td>
    <td valign="top" align="left">
      <h5>4 stops =&gt; ~ 1 stop per zone</h5>
    </td>
  </tr>
</table>

<h5>Suspicious that I might be measuring the camera's 8-bit analog to digital
conversion rather than effective DR, I went on the the single scene test described <a href="#test2">above</a>.&nbsp;</h5>

<div align="left">
  <table border="0" cellspacing="0" cellpadding="0">
    <tr>
      <td valign="bottom"><a href="index.htm#site_index"><img border="0" src="art_index.gif" width="133" height="34"></a></td>
      <td valign="bottom"><a href="#page_index"><img border="0" src="up.gif" width="41" height="51"></a></td>
      <td valign="bottom"><a href="filters.htm"><img border="0" src="next_art.gif" width="133" height="34"></a></td>
    </tr>
  </table>
</div>

<hr>

<h2><a name="tonality"></a><b>Tonality</b></h2>

<p><a href="./#warranty"><em><strong><img
src="underconst.gif"
alt="Marks areas under contruction--stay tuned. Click to review Limited Warranty section on the home page."
align="baseline" border="0" width="24" height="15"></strong></em></a>  Under construction...</p>

<p>Photographically speaking, tonal variation or <i>tonality</i> refers to the
range and distribution of light and dark in a scene or in a grayscale (B&amp;W)
or color image. Tonality can be an extraordinarily powerful visual element, as anyone struck
by an Ansel Adams B&amp;W photograph will attest.</p>

<p>On the digital side, galleries like</p>

<ul>
  <li>
    <p style="margin-bottom: 6"><a href="http://homepage.mac.com/scho/title.html">Digital
    Grey</a>�B&amp;W Nikon CoolPix 950 images by <b>dp<i>FWIW</i></b>
    contributor <a href="index.htm#schofield">Carl Schofield</a>.&nbsp;</li>
  <li><a href="http://www.animalu.com/pics/photos.htm">Jeff Alu's</a> collection
    of B&amp;W Kodak DC280 images</li>
</ul>

<p>beautifully demonstrate the fruits of taking control of tonality.</p>

<p>Digital tonal control begins at the scene with <a href="#previsualization">pre-visualization</a>
of the final image to be produced and ends in post-processing. Due to <a href="#dynamic">dynamic range</a> limitations in both
humans and
cameras, tonality and preservation of detail go hand-in-hand: The more extreme
the tone, the less detail can be seen within it. In fact, concern over detail
often drives the exposure decision, particularly with regard to highlights and deep
shadows.&nbsp;</p>

<p>Post-processing adds fine tuning and the opportunity to accommodate tonal
ranges well beyond the <a href="#dynamic">dynamic range</a> of the camera, as
noted <a href="#blending">above</a>.&nbsp;</p>

<h5>Technical note: Film
developing methods similarly extend the dynamic range of film, but largely in
the opposite direction. With film, you generally expose for the shadows and
develop for the highlights; with digital recording, you assiduously avoid
blowing out the highlights and bring up the shadows as needed in
post-processing.&nbsp;</h5>

<table border="0">
    <tr>
        <td valign="top"><em><strong><a href="#thumb"><img src="bypass.gif"
        alt="Marks opportunities to bypass long-winded discussions and cut to the action line. Click to review Limited Warranty section on the home page."
        align="texttop" border="0" width="36" height="30"></a></strong></em></td>
        <td valign="top">Click at left to cut to <a href="#thumb">manual
          exposure rules of thumb</a> now. To dive headlong into tonality, read on.</td>
    </tr>
</table>

<hr>

<h3><b><a name="metering_basics"></a>Metering for Medium Tone</b></h3>

<p>To begin to understand and exert tonal control, you must first become one
with this immutable fact of photographic life:</p>

<blockquote>
  <p><b><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;All
  reflective TTL metering systems in digital and film cameras are designed to
  indicate an exposure that will render the metered target region in a medium
  tone, <i>regardless</i> of its absolute or apparent luminance or color.</b></p>

</blockquote>
<p>That's right�follow the meter's advice, and your metered target will end up
a medium tone, no matter the color and no matter how light or dark it might
appear in the flesh.&nbsp;</p>

<p>Believe it or not, that turns out to be a very reasonable approach to
metering�once you learn to <a href="#working">make it work for you</a> instead
of against you.</p>

<p>The first step is to know what a medium tone looks like, since
that's what the meter's dishing up:</p>

  <table border="2" height="44" width="913">
    <tr>
      <td valign="top" align="left" colspan="2" width="901">
        <h4><a name="medium"></a><b>Medium
        Tone</b></h4>
      </td>
    </tr>
    <tr>
      <td valign="top" align="left" width="50%">For grayscale metering purposes,
        the medium tone is <i>medium</i> or <i>middle gray</i>, which by
        definition reflects 18% of incident light. In 8-bit recording and
        display systems with 256 shades of gray, the RGB triad {127, 127, 127}
        shown at right closely approximates medium gray. <a href="#medium_colors"> Medium color tones</a> have
        the same reflectance as medium gray.</td>
      <td valign="top" align="left" bgcolor="#7F7F7F" width="50%">&nbsp;</td>
    </tr>
  </table>

<p>According to John Shaw, the best reason to carry a <a href="#gray_card">gray card</a> is
simply to have a reliable medium-toned comparison at hand.&nbsp; Tony Sparado's <a href="http://home.nc.rr.com/tspadaro/The_Grey_Card.html">The
Gray Card</a> tutorial ends up saying the same thing.</p>

<h4><a name="gray_card"></a>The Gray Card Approach</h4>

<p>If your meter's so obsessed with medium tones, why not give it one?</p>

<p>If you meter off a known medium-toned sample held in the light illuminating
your subject, everything in the frame <i>in that same light</i> will be,
technically speaking, properly exposed. Objects in the frame receiving more or
less light than that will be over- or underexposed accordingly, but your subject
will be taken care of.</p>

<p>Many serious photographers carry an &quot;18% gray&quot; or &quot;medium
gray&quot; card for just this purpose. See Tony Sparado's <a href="http://home.nc.rr.com/tspadaro/The_Grey_Card.html">The
Gray Card</a> for an entertaining tutorial on using one effectively. The <a href="http://www.nyip.com/">New
York Institute of Photography</a> also offers a worthwhile <a href="http://www.nyip.com/tips/tip_graycard.html">gray
card tutorial</a>.&nbsp;</p>

<blockquote>

<p><b><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;Make sure
your gray card and subject both have the same orientation to your light source
before metering.</b></p>

</blockquote>

<p>Gray cards are getting hard to find these days, even in high-end photography
shops, but there are many workable substitutes. If your printer is properly
calibrated, you can print one yourself from a gray fill set at RGB(127, 127,
127). The average Caucasian palm is about one full stop lighter
than a gray card. Don't look now, but your camera bag may well be medium-toned,
too.</p>

<h4>The Spot-Meter Approach</h4>

<p>The <a href="#gray_card">gray card approach</a> just described in effect keys
on the lighting in the scene, but it's not always feasible to meter off a gray
card in the light bathing your subject, particularly if that light is far away
or otherwise inaccessible. (What's the chance of that bird allowing your
assistant to hold a gray card next to its head?)</p>

<p>A less exact but far more flexible approach based on <a href="#spot">spot-metering</a>
keys instead on your knowledge of <a href="#tweaks">subject reflectance</a> and
the <a href="#adjust">tonal range</a> available in your digital camera. <a href="#bracketing">Bracketing</a>
can easily make up for the uncertainties involved. Making this approach work is the
thrust of the remainder of this section on tonality. In challenging situations,
the gray card and spot metering approaches can be combined.</p>

<h4><a name="snow"></a>Getting Whiter Whites and Blacker Blacks</h4>

<p>If you <a href="#spot">spot meter</a> on
fresh snow and use the exposure indicated by the meter, the
snow will turn out medium gray, not white. To end up with
the bright white snow you know you saw that day, you have to <i>overexpose</i>
the snow. Many
find this approach counterintuitive at first, but the same applies to any white
or near-white object, as this <a href="flowers.htm#lily_series">cala lily series</a>
illustrates.&nbsp;<a href="#ec">Exposure compensation</a> is usually the
simplest way to pull this off.</p>

<p>Conventional (film-based) photographic wisdom advises 1-2 stops of overexposure to keep white snow white, but on the digital side,
that may be too much, particularly for cameras with limited <a href="#dynamic">dynamic
range</a>. Just how much overexposure to dial in is best determined by <a href="#bracketing">bracketing</a>,
but be sure to base your bracketing on a <i>spot</i> metering of the snow. If
you meter the entire scene and include dark elements like pine trees, your may
end up with blown-out snow highlights at well under a stop of
overexposure.&nbsp;</p>

<div align="left">
  <table border="0">
    <tr>
      <td valign="top" align="left"><a name="lava"></a>The opposite approach
        works on the
        dark side. When I shot the nearly black Hawaiian basalt at right with my
        automatic-only Oly D-340L point-and-shoot in early 1999, I had no choice
        but to accept the meter's exposure, and out
        came medium gray.
        <p>To capture the lava's extremely dark tone, I would
        have had to <i> underexpose</i> it by at least 2 stops. My current C-2020Z would have
        been more than happy to oblige.</td>
      <td valign="top" align="left"><a href="images/lava-fern.jpg"><img border="0" src="images/lava-fern0.jpg" alt="Fern emerging from frozen lava whirlpool, Napau Crater Trail, Hawaii Volcanoes Nat'l Park. Click to see 1280x960 original. [D-340L]" width="320" height="240"></a></td>
    </tr>
  </table>
</div>
<p>For more examples, see the table of <a href="#tweaks">subject-based exposure
tweaks</a> below.</p>

<h4><b><a name="medium_colors"></a>What About Colors?</b></h4>

<p>Colors are equally subject to the medium tone imperative. If you
        meter the dark green canopy of a conifer forest and don't intervene,
        it'll end up medium green. But with a 1-stop underexposure, the captured
green
        will probably match your perception at the scene.</p>

<h4><b>Manual vs. Priority Modes</b></h4>

<p>On a malleable camera like the Oly C-2020Z, these calculated over- and
underexposures relative to meter indications can be executed</p>

<ul>
  <li>
    <p style="margin-bottom: 9">with complete freedom in manual exposure
mode, or</li>
  <li>with a �2-stop leeway via <a href="#ec">exposure compensation</a>  (EC) in a <a href="#priority"> priority</a>
    mode.</li>
</ul>
<p>The much more convenient priority/EC approach limits you to �2 stops of
departure from the meter, but if your camera realistically has only 4-5 <a href="#stops">stops</a> of
effective <a href="#dynamic">dynamic range</a>, that may be all you need.</p>

<hr>

<h3><b><a name="working"></a>Working Off the Medium Tone</b></h3>

<p>Unhelpful as it might seem, the meter's fetish with medium tones turns out to be just the rigid framework needed to build a rational scheme for
tonal control at exposure time. Think of it as your place to stand when you play
the exposure game.</p>

<p>Here are the basic building blocks as I see them:</p>

<ul>
  <li>
    <p style="margin-bottom: 9">Know a medium tone when you see one. Carry an <a href="#gray_card">18%
    gray card</a> as a reference.</li>
  <li>
    <p style="margin-bottom: 9">Learn to recognize deviations from medium tones and the number of stops of
    exposure adjustment they represent <i>on your camera.</i> The <a href="#zone">zone
    system</a> provides a useful way to think and talk about such things.</li>
  <li>Learn to work out a balanced exposure strategy based on <a href="#previsualization">pre-visualization</a>
    of the final image. Take the entire the image
    into account�particularly the main subject and the shadows and highlights
    containing detail to be recorded. Your goal should be a prioritized best-fit
    solution for subject, highlight and shadow <a href="#tonality">tonalities</a>.</li>
</ul>
<p>Let's tackle these tonality control measures one by one.</p>
<h4><b><a name="hold"></a>First Do No Harm</b></h4>

<p>If you don't know a <a href="#medium"> medium tone</a> when you see one, you run the risk of making
unnecessary exposure tweaks leading to unwelcome results. If your subject
is medium-toned and you'd like to show it that way, there's no need to
override the meter�at least not on that account alone.</p>

<p>As noted above, the best reason to carry a <a href="#gray_card">gray card</a> is to have a reliable
medium-toned comparison at hand, but any <i>known</i> medium-toned
object will do. Your camera bag may well fill the bill.</p>

<h4><a name="adjust"></a><b>Adjust for Desired Tonality</b></h4>

<p>To control tonality, you'll also need a way to gauge departures from medium tones and to estimate
the exposure adjustments needed to reproduce them. For this purpose, it's useful
to divide tone and detail levels into a manageable number of discrete steps
ranging from featureless black to featureless white, and to relate these steps to deviations
from meter readings in stops, as in the sample tone vs. exposure table below.</p>

<p>Photographers often
refer to such tonal steps as <i><a href="#zone_table">zones</a></i>. Note that
these gradations and stops will apply to shades of gray and colors alike.</p>

<p>For a camera with a 5-stop effective DR, a +2-stop adjustment in the <a href="#snow">snow
example</a>  above would have &quot;placed&quot; the snow on an &quot;extremely
light&quot; tone (Zone 9), as illustrated in the table below. Likewise, metering a red car and adding a
stop of exposure would render
it a light red (Zone 7). Reducing exposure by 2 stops would produce an extremely dark red
rendition of the same car (Zone 1). However, you'd have to use proportionately
larger exposure corrections to achieve the same results with a camera with a
wider effective DR.</p>

<div align="left">
  <table border="2" width="662">
    <tr>
      <td valign="top" align="left" colspan="5" width="650">
        <h4><b><a name="tone_table"></a>Tone vs. Exposure Table for a Camera
        With a 5-Stop DR&nbsp;</b></h4>
      </td>
    </tr>
    <tr>
      <td valign="top" align="left" width="89"><b>Sample&nbsp;</b></td>
      <td valign="top" align="left" width="62"><b><a href="#zone">Zone</a>&nbsp;</b></td>
      <td valign="top" align="left" width="161"><b>Tone&nbsp;</b></td>
      <td valign="top" align="left" width="200"><b>Texture&nbsp;or Detail&nbsp;</b></td>
      <td valign="top" align="left" width="114"><b>Stops Off Meter&nbsp;</b></td>
    </tr>
    <tr>
      <td valign="top" align="left" bgcolor="#FFFFFF" width="89">&nbsp;</td>
      <td valign="top" align="center" width="62">10</td>
      <td valign="top" align="left" width="161">solid white</td>
      <td valign="top" align="left" width="200">long gone</td>
      <td valign="top" align="center" width="114">+2�</td>
    </tr>
    <tr>
      <td valign="top" align="left" bgcolor="#E6E6E6" width="89">&nbsp;</td>
      <td valign="top" align="center" width="62">9</td>
      <td valign="top" align="left" width="161">extremely light&nbsp;</td>
      <td valign="top" align="left" width="200">just gone</td>
      <td valign="top" align="center" width="114">+2</td>
    </tr>
    <tr>
      <td valign="top" align="left" bgcolor="#CCCCCC" width="89">&nbsp;</td>
      <td valign="top" align="center" width="62">8</td>
      <td valign="top" align="left" width="161">very light</td>
      <td valign="top" align="left" width="200">barely discernable</td>
      <td valign="top" align="center" width="114">+1�</td>
    </tr>
    <tr>
      <td valign="top" align="left" bgcolor="#B4B4B4" width="89">&nbsp;</td>
      <td valign="top" align="center" width="62">7</td>
      <td valign="top" align="left" width="161">light</td>
      <td valign="top" align="left" width="200">substantial</td>
      <td valign="top" align="center" width="114">+1</td>
    </tr>
    <tr>
      <td valign="top" align="left" bgcolor="#9A9A9A" width="89">&nbsp;</td>
      <td valign="top" align="center" width="62">6</td>
      <td valign="top" align="left" width="161">medium light</td>
      <td valign="top" align="left" width="200">full</td>
      <td valign="top" align="center" width="114">+�</td>
    </tr>
    <tr>
      <td valign="top" align="left" bgcolor="#7F7F7F" width="89">&nbsp;</td>
      <td valign="top" align="center" width="62">5</td>
      <td valign="top" align="left" width="161">medium</td>
      <td valign="top" align="left" width="200">full (meter reading)</td>
      <td valign="top" align="center" width="114">0</td>
    </tr>
    <tr>
      <td valign="top" align="left" bgcolor="#646464" width="89">&nbsp;</td>
      <td valign="top" align="center" width="62">4</td>
      <td valign="top" align="left" width="161">medium dark</td>
      <td valign="top" align="left" width="200">full</td>
      <td valign="top" align="center" width="114">-�</td>
    </tr>
    <tr>
      <td valign="top" align="left" bgcolor="#4A4A4A" width="89">&nbsp;</td>
      <td valign="top" align="center" width="62">3</td>
      <td valign="top" align="left" width="161">dark</td>
      <td valign="top" align="left" width="200">substantial</td>
      <td valign="top" align="center" width="114">-1</td>
    </tr>
    <tr>
      <td valign="top" align="left" bgcolor="#333333" width="89">&nbsp;</td>
      <td valign="top" align="center" width="62">2</td>
      <td valign="top" align="left" width="161">very dark</td>
      <td valign="top" align="left" width="200">barely discernable&nbsp;</td>
      <td valign="top" align="center" width="114">-1�</td>
    </tr>
    <tr>
      <td bgcolor="#181818" width="89">&nbsp;</td>
      <td align="center" width="62">1</td>
      <td width="161">extremely dark</td>
      <td width="200">just gone</td>
      <td align="center" width="114">-2</td>
    </tr>
    <tr>
      <td bgcolor="#000000" width="89">&nbsp;</td>
      <td align="center" width="62">0</td>
      <td width="161">solid black</td>
      <td width="200">long gone</td>
      <td align="center" width="114">-2�</td>
    </tr>
  </table>
</div>
<p>In this table, the � stop per zone deviations from a
medium-toned (Zone 5) metered exposure add up to a 5-stop effective DR�one
typical of color slide film. However, many B&amp;W films and at least some
digital cameras with effective DRs of 7-8 stops run closer to 1 stop per zone. <a href="#testing">Testing</a>
is the only way to know how to relate zones and stops for your camera.</p>

<h4><b><a name="tonal_control"></a>Balanced
Tonal Control</b></h4>

<p>Keep in mind that adjusting exposure to render one object in a certain
tone can have a negative impact on other image elements.&nbsp;Shadow and
highlight details are most at risk.&nbsp;</p>

<p> To guard against
trashing detail you'd like to preserve, consider this 4-step approach to tonal
control based on a tone-exposure table like the one <a href="#tone_table">above</a>.</p>

<ol>
  <li>
    <p style="margin-bottom: 9">Spot-meter the <b>main subject</b> and work out an appropriate exposure
    adjustment to render it with the desired tone and detail. In <a href="#zone">zone
    system</a> parlance, one speaks of &quot;placing&quot; the subject in a
    particular <a href="#zones">zone</a>.*</li>
  <li>
    <p style="margin-bottom: 9">Spot-meter the <b>brightest highlights</b> containing detail to be
    preserved to make sure they're less than half the camera's effective DR
    above the subject exposure
    determined in Step 1.&nbsp;If the camera's DR is 7 stops, stay within 3
    stops. Any farther out, and you'll risk losing highlight
    detail.</li>
  <li>
    <p style="margin-bottom: 9">Spot-meter the <b>darkest shadows</b> containing detail to be preserved to
    make sure they're less than half the camera's effective DR below the subject exposure determined in
    Step 1. Any farther out, and you'll risk losing shadow detail.</li>
  <li>
    <p style="margin-bottom: 9">Before shooting, <b> juggle</b> the subject, highlight
    and shadow exposure
    adjustments as dictated by your photographic intent and your camera's
    effective DR.</li>
  <li>If you find that you can't encompass all the detail you need to preserve in
    a single exposure, you've got <a href="#excess_contrast">excess contrast</a>
    on your hands. Consider <b>reducing the contrast</b>
    with <a href="#fill">fill flash</a>, a <a href="#reflectors">reflector</a>
    or a suitable <a href="#filters">filter</a>. Failing that, consider <a href="#blending">image
    blending</a> in <b>post-processing</b>.&nbsp;</li>
</ol>
<p>* Note that the desired target tone in Step 1 doesn't have to match your
perception at the scene. As long as the fallout remains tolerable, you're free
to choose any tone that strikes your fancy.</p>

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<hr>

<h2><a name="zone"></a><b>The Zone System</b></h2>

<p>In the 1930s, legendary B&amp;W photographer Ansel Adams invented the <i>zone system�</i>an
elaborate but spectacularly successful <a href="#tonal_control"> tonal control</a> method for negative film.
For starters, his approach demanded meticulous
calibration of all components of the photographic process, from lens and film choice
through exposure to paper selection and development technique.&nbsp;Application
in the field required <a href="#previsualization">pre-visualization</a>
of the final image�in Adam's case, the B&amp;W print�followed by careful
juggling of the exposure to realize the desired print.</p>

<p>Since then, the zone system has been extended to other photographic arenas,
including color transparency film and now digital capture systems. For more details on the zone system in B&amp;W digital photography, see the
excellent August, 2000 digitalFOTO magazine article cited <a href="index.htm#books">here</a>.&nbsp;</p>

<hr>

<h3><a name="zones"></a>The Zones</h3>

<p>To codify tonality and simplify exposure calculations, Adams divided the tonal
ranges he wished to target in his photographs into 9 distinct <i>zones</i> he numbered with Roman numerals
I-IX. The zones are distinguished on the basis of tone&nbsp; and texture. Many zone practitioners now recognize 11 zones numbered 0-10, as shown in
the table below:</p>

<div align="left">
  <table border="2" width="674">
    <tr>
      <td valign="top" align="left" colspan="5" width="662">
        <h4><a name="zone_table"></a><b>Zones for a 1 Stop Per Zone Camera</b></h4>
      </td>
    </tr>
    <tr>
      <td valign="top" align="left" width="90"><b>Sample&nbsp;</b></td>
      <td valign="top" align="left" width="67"><b>Zone&nbsp;</b></td>
      <td valign="top" align="left" width="170"><b>Tone&nbsp;</b></td>
      <td valign="top" align="left" width="200"><b>Texture&nbsp;or Detail&nbsp;</b></td>
      <td valign="top" align="left" width="111"><b>Stops Off&nbsp;
        Meter&nbsp;&nbsp;</b></td>
    </tr>
    <tr>
      <td valign="top" align="left" bgcolor="#FFFFFF" width="90">&nbsp;</td>
      <td valign="top" align="center" width="67">10</td>
      <td valign="top" align="left" width="170">solid white</td>
      <td valign="top" align="left" width="200">long gone</td>
      <td valign="top" align="center" width="111">+5</td>
    </tr>
    <tr>
      <td valign="top" align="left" bgcolor="#E6E6E6" width="90">&nbsp;</td>
      <td valign="top" align="center" width="67">9</td>
      <td valign="top" align="left" width="170">extremely light&nbsp;</td>
      <td valign="top" align="left" width="200">just gone</td>
      <td valign="top" align="center" width="111">+4</td>
    </tr>
    <tr>
      <td valign="top" align="left" bgcolor="#CCCCCC" width="90">&nbsp;</td>
      <td valign="top" align="center" width="67">8</td>
      <td valign="top" align="left" width="170">very light</td>
      <td valign="top" align="left" width="200">barely discernable</td>
      <td valign="top" align="center" width="111">+3</td>
    </tr>
    <tr>
      <td valign="top" align="left" bgcolor="#B4B4B4" width="90">&nbsp;</td>
      <td valign="top" align="center" width="67">7</td>
      <td valign="top" align="left" width="170">light</td>
      <td valign="top" align="left" width="200">substantial</td>
      <td valign="top" align="center" width="111">+2</td>
    </tr>
    <tr>
      <td valign="top" align="left" bgcolor="#9A9A9A" width="90">&nbsp;</td>
      <td valign="top" align="center" width="67">6</td>
      <td valign="top" align="left" width="170">medium light</td>
      <td valign="top" align="left" width="200">full</td>
      <td valign="top" align="center" width="111">+1</td>
    </tr>
    <tr>
      <td valign="top" align="left" bgcolor="#7F7F7F" width="90">&nbsp;</td>
      <td valign="top" align="center" width="67">5</td>
      <td valign="top" align="left" width="170">medium</td>
      <td valign="top" align="left" width="200">full (meter reading)&nbsp;</td>
      <td valign="top" align="center" width="111">0</td>
    </tr>
    <tr>
      <td valign="top" align="left" bgcolor="#646464" width="90">&nbsp;</td>
      <td valign="top" align="center" width="67">4</td>
      <td valign="top" align="left" width="170">medium dark</td>
      <td valign="top" align="left" width="200">full</td>
      <td valign="top" align="center" width="111">-1</td>
    </tr>
    <tr>
      <td valign="top" align="left" bgcolor="#4A4A4A" width="90">&nbsp;</td>
      <td valign="top" align="center" width="67">3</td>
      <td valign="top" align="left" width="170">dark</td>
      <td valign="top" align="left" width="200">substantial</td>
      <td valign="top" align="center" width="111">-2</td>
    </tr>
    <tr>
      <td valign="top" align="left" bgcolor="#333333" width="90">&nbsp;</td>
      <td valign="top" align="center" width="67">2</td>
      <td valign="top" align="left" width="170">very dark</td>
      <td valign="top" align="left" width="200">barely discernable&nbsp;</td>
      <td valign="top" align="center" width="111">-3</td>
    </tr>
    <tr>
      <td bgcolor="#181818" width="90">&nbsp;</td>
      <td align="center" width="67">1</td>
      <td width="170">extremely dark</td>
      <td width="200">just gone</td>
      <td align="center" width="111">-4</td>
    </tr>
    <tr>
      <td bgcolor="#000000" width="90">&nbsp;</td>
      <td align="center" width="67">0</td>
      <td width="170">solid black</td>
      <td width="200">long gone</td>
      <td align="center" width="111">-5</td>
    </tr>
  </table>
</div>
<h5>Table Note: I've abandoned Roman numerals to simplify my own zone thinking.
The Romans never used zeroes, anyway.</h5>

<p>Whether you settle on 9 zones or 11, the critical piece of the puzzle is a
realistic number of <i>stops per zone</i> for your camera, and that relates
directly to its <a href="#dynamic">effective dynamic range</a>�here the number
of stops of exposure separating the top of Zone 8 from the bottom of Zone 2.</p>

<p>Exposing an object according to its <a href="#spot">spot meter</a> reading
amounts to placing it squarely on Zone 5, the <a href="#medium">medium tone</a>
with which the meter is obsessed. To place it on Zone 8 and turn it into a
highlight instead, you'd have to override the meter and
increase exposure by 8 - 5 = 3 times the number of stops per zone your camera
provides.</p>

<p> Through
the judicious adjustment of exposure based on spot meter readings, Adams could &quot;place&quot;
snow &quot;on Zone 9&quot; or a shadowed rock with detail to be preserved
&quot;on Zone 3&quot; to achieve a <a href="#previsualization">pre-visualized</a>
tonal range in his final B&amp;W print.</p>

<hr>

<h3>Zoning Requirements</h3>

<p>Adams succeeded in reproducing his tonal <a href="#previsualization">pre-visualizations</a>
only by virtue of his meticulous preparation, which included careful calibration of his lenses, cameras, films, developing processes and
photographic papers. With the testing came the predictability that made his
pre-visualizations attainable.</p>

<h4>What You'll Need To Get Started</h4>

<p>Fortunately, you don't have to adopt the zone system whole-hog to benefit
from its most important principles, as we'll see in the next few
subsections. To get started, you'll need&nbsp;</p>

<ul>
  <li>
    <p style="margin-bottom: 9">A digital zoom camera with a
decent <a href="#spot"> spot meter</a> and full manual exposure control</li>
  <li>
    <p style="margin-bottom: 9">A clear understanding of the camera's effective <a href="#dynamic">dynamic
    range</a> and stops per zone</li>
  <li>
    <p style="margin-bottom: 9">A competent digital image editor with tone
    curves and layers.</li>
</ul>

<p>The second item will allow you to make your own <a href="#zone_table">zone
vs. exposure table</a>. Only then can you manipulate tonality in a predictable
way. With a digital camera, it's relatively easy to construct such a table based
on the simple <a href="#testing">DR testing procedure</a>
described above.&nbsp;</p>

<h4>Full-Blown Zone&nbsp;</h4>

<p>On
the exposure side, full-blown application of the zone system requires an expensive narrow-angle (preferably 1�) external
spot meter.
Calibration of camera <a href="#iso">ISO</a> to the external meter is an essential
first step.</p>

<p>On the printing side, thorough zone technique will involve the testing and
calibration of monitors, printers, inks and papers as well. Such matters are currently well beyond my
experience.</p>

<hr>

<h3><a name="zone_upsidedown"></a>The Zone Dictum Turned Upside Down</h3>

<p>For negative film, the zone system is often neatly summarized in the dictum &quot;Meter for the shadows, develop for the highlights,&quot; but that hardly
does justice to a method that by all accounts takes years of patient practice to
master.&nbsp;</p>

<p> With negative film, desired shadow detail sets an exposure floor.
Exposing above that floor increases aperture or exposure time with concomitant
reductions in <a href="#dof">DOF</a> and motion suppression�typically with little
other gain in the shadows. Dialing in the highlights can generally be left to
the development process.</p>

<h4>The Digital Ceiling</h4>

<p>The film-based zone dictum turns out to be bad advice when it comes to CCD
cameras, which handle high exposures
with considerably less grace than negative film. Nasty CCD behaviors like <a href="#bloomng"> blooming</a> and
the draining off of &quot;excess&quot; photoelectrons when sensels get
&quot;full&quot; effectively truncate the upper end of their otherwise fairly
linear charge-exposure (characteristic) curves.</p>

<p>Thus, to avoid complete loss of highlight detail,</p>

<blockquote>
  <p><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;<b>It's
  generally safer to expose the highlights to fall on Zone 7-8 and
  post-process the shadows on the digital side.</b></p>

</blockquote>
<p>In other words, desired highlight detail sets a <i>ceiling</i> on digital
exposure. You then bring up the shadows as needed with gamma adjustments or the more
sophisticated tone curves found in advanced editors like PhotoShop and PHOTO-PAINT. You may well make shadow noise more conspicuous in
the process, but that's usually preferable to glaring blown-out highlights. More
advanced post-processing techniques addressing <a href="#dynamic">dynamic range</a>
are discussed <a href="#blending">above</a>.</p>

<p>Editing tools can always be used to tweak tonality after the fact to good
advantage, but keep in mind that</p>

<table border="0">
    <tr>
        <td valign="top"><a href="index.htm#warranty"><em><strong><img src="tumbling_arrow.gif" alt="Marks the gotchas" align="left" border="0" hspace="0" width="16" height="16"></strong></em></a></td>
        <td valign="top"><i><b>If you blow out the highlights or lose the shadow
          detail in the process of placing something else on a specific zone at
          exposure time, you probably won't be able to salvage them in
          post-processing.</b></i></td>
    </tr>
</table>

<p>That's the No. 1 challenge once you take charge of <a href="#tonality">tonality</a>.&nbsp;</p>

<hr>

<h3><a name="previsualization"></a>Pre-visualization is the Key</h3>

<p>In the field, zone system technique begins with a <i>pre-visualization</i> of
the final image to determine which scene elements belong in which zones.&nbsp;</p>

<p>With a digital camera, highlights with detail to be preserved must go to Zone
7 or Zone 8, as discussed <a href="#zone_upsidedown">above</a>. An exposure
consistent with all the desired zone placements must then be concocted based the
number of stops per zone the camera provides. Efforts to reduce <a href="#excess_contrast">excess
contrast</a> may be necessary to reach a workable exposure solution.&nbsp;</p>

<p>I can't improve on Bob Hickman's excellent zone system tutorial <a href="http://www.apogeephoto.com/mag2-6/mag2-7rh.shtml">Using
the Zone System in the Field</a>, which nicely illustrates the concept and practice of
pre-visualization.</p>

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<hr>

<h2><a name="thumb"></a><strong>Manual Exposure Rules of Thumb</strong></h2>

<p>Collected here are a number of tricks to get you in the ballpark with
exposure. If nothing else, they're useful cross-checks on the accuracy of your
camera's TTL metering system and <a href="#iso">ISO settings</a>.</p>

<hr>

<h3><b><a name="sunny"></a>The Sunny f/16 Rule, Digital Style</b></h3>

<p>When close-ups aren't involved, film photographers find the &quot;sunny
f/16&quot; exposure rule fairly reliable:</p>

<blockquote>

<p><b>In direct bright midday sunlight, correct exposure of a medium-toned frontlit
subject at f/16 will require the shutter speed nearest 1/ISO,</b></p>

</blockquote>
<p>where ISO is the film-camera system's <i>true</i> ISO rating. Add a stop for
a sidelit subject.</p>

<p>Note again that the true ISO of a particular film-camera combination and the
nominal ISO marked on the film aren't any more likely to match than a digital camera's
true and nominal ISO. &quot;Correct exposure&quot; in this context means that a
medium-toned subject like an 18% gray card will appear medium-toned in the
resulting photograph.&nbsp;</p>

<p>At ISO 100, this amounts to an <a href="#ev">EV</a> of 14.6. By <a href="#reciprocity">reciprocity</a>,
any aperture and shutter speed yielding EV 14.6 satisfies the rule.</p>

<h4>The Digital Version</h4>

<p>To the extent that digital ISOs equal film ISOs, the same EV 14.6 rule applies to
digital cameras as well. But since the diffraction-limited lenses found in most
consumer digital cameras generally preclude f/16 apertures, a
reciprocity-adjusted digital version would be handier:&nbsp;</p>

<div align="left">
  <table border="2">
    <tr>
      <td>
        <h4><a href="index.htm#warranty"><img src="diamond.gif"
alt="Marks the paydirt" border="0" width="15" height="15"></a>&nbsp;<b>Sunny
        f/5.6 Rule For Digital Cameras (EV 14.6)</b></h4>
      </td>
    </tr>
    <tr>
      <td>

<p>In direct bright midday sunlight, proper exposure of a medium-toned frontlit
subject at f/5.6 will require the shutter speed nearest 1/(8 * ISO), where ISO
is the digital camera's <i>actual</i> ISO. Add a stop for a sidelit subject.</p>

      </td>
    </tr>
  </table>
</div>

<p>In other words, your meter should give something equivalent to f/5.6 @ 1/800
sec on a clear sunny day for a medium-toned frontlit subject if your camera's
ISO 100 setting is accurate.</p>

<p><a name="iso_actual"></a> Set at a nominal ISO of 100, my Oly C-2020Z
consistently wants the equivalent of f/5.6 @ 1/650 sec. I take this to mean that
its actual ISO is closer to 80 when it's set for ISO 100.</p>

<p>I haven't tested the sunny f/5.6 rule with other cameras. If you do, I'd love
to hear how it works out at <a
href="mailto:dpFWIW@cliffshade.com">dp<i>FWIW</i>@cliffshade.com</a>.</p>

<hr>

<h3><b><a name="bracketing"></a>Bracketing</b></h3>

<p>When in doubt, take exposures on either side of your best
guess. This safety measure is known as <i>bracketing</i>. The Blacklocks (full
citation <a href="index.htm#books">here</a>) recommend bracketing for exposure by 2/3 stop.
Assuming you're not more than a stop off the mark to begin with, this will leave
you no more than 1/3 stop away from the ideal with only 2 extra shots.</p>

<p><a href="#priority">Priority modes</a> and <a href="#ec">exposure
compensation (EC) controls</a> make bracketing a snap. My Oly C-2020Z even has a
flexible auto-bracketing feature that can be set to take 3-5 shots covering up
to 1 stop above and below the current exposure in even steps, but <a href="#ec">EC</a>
makes exposure bracketing so easy, I haven't felt a need to try it.</p>

<h4>Bracketing's Not Just About Exposure</h4>

<p>The bracketing habit has served me well. So well, in
fact, I've found it very useful to extend the concept to
other practical photographic issues like <a href="#steadiness">steadiness</a>, <a href="#resolving">resolving power</a>,
<a href="#wb">white balance</a>, <a href="#tonality">tonality</a>,
<a href="filters.htm">filters</a>, <a href="c-2000z/lenses/index.htm">conversion
lenses</a> and even composition�especially in macro mode. With enough time, memory and battery power
along, the marginal cost of another shot or ten is zero. I'm still far from
being able to predict which shot will come out best with any reliability.&nbsp;</p>

<hr>

<h3><b><a name="tweaks"></a>Tonality Tweaks</b></h3>

<p><a href="./#warranty"><em><strong><img
src="underconst.gif"
alt="Marks areas under contruction--stay tuned. Click to review Limited Warranty section on the home page."
align="baseline" border="0" width="24" height="15"></strong></em></a>   Under construction...</p>

<p>Now that you're attuned to <a href="#tonality">tonality</a>,
here are some exposure adjustment guidelines gleaned from books by John Shaw and
the Blacklocks (click <a href="index.htm#books">here</a> for full citations):</p>

<div align="left">
  <table border="2">
    <tr>
      <td colspan="4" valign="top">
        <h4><b>tonality adjustments </b>(after
        spot-metering on the subject)</h4>
      </td>
    </tr>
    <tr>
      <td valign="top"><b>subject&nbsp;</b></td>
      <td valign="top"><b>target tone (zone)&nbsp;</b></td>
      <td valign="top"><b>tweak (stops)&nbsp;</b></td>
      <td valign="top"><b>notes&nbsp;</b></td>
    </tr>
    <tr>
      <td valign="top">flower, middle tone</td>
      <td align="center" valign="top">medium light (VI)</td>
      <td align="center" valign="top">+1/2</td>
      <td valign="top">no direct sun involved</td>
    </tr>
    <tr>
      <td valign="top">flower, white&nbsp;</td>
      <td align="center" valign="top">very light (IX)</td>
      <td align="center" valign="top">+1-2</td>
      <td valign="top">no direct sun involved</td>
    </tr>
    <tr>
      <td valign="top">snow</td>
      <td align="center" valign="top">very light (IX)</td>
      <td align="center" valign="top">+1-2</td>
      <td valign="top">to make snow white</td>
    </tr>
    <tr>
      <td valign="top">sunrise, sunset&nbsp;</td>
      <td align="center" valign="top">light (VII)</td>
      <td align="center" valign="top">+1</td>
      <td valign="top">meter on sky away from sun&nbsp;</td>
    </tr>
  </table>
</div>
<p>Before committing to any of these suggestions, be sure think
through the consequences for all the other important elements in your scene. <a href="#bracketing">Bracket</a>
as needed.</p>

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<hr>

<h2><a name="advanced"></a><strong>Advanced Digital Exposure
Considerations</strong></h2>

<p>In response to one my many attempted brain-pickings, <b>dp<i>FWIW</i></b>
contributor <a href="index.htm#lackamp">Tom Lackamp</a> wrote of the exposure
challenges shared by slide film and digital photographers, here in the context of intentional
underexposure in flower photography: </p>

<blockquote>
<h5>That's the normal &quot;modus operandi&quot; when you're shooting slide film.
Most folks (myself included) consistently underexpose(d) slide film by 1/2 stop
or so to increase color saturation a bit. When shooting people under controlled
lighting conditions, however, we shoot pretty much at its rated speed so you <i>don't</i> oversaturate skin tones. (You treat color negative film exactly the
opposite: overexpose by about 1/2 stop [or more] to increase saturation, and
shoot skin tones in good lighting at its rated speed.)</h5>
<h5>The problem with this approach, for slide film, is that you dangerously
decrease your margin for error. Slide film has very little latitude to begin
with, and underexposing, even a little bit, cuts deeply into that margin. Go
just a bit deeper than you should and you lose those sparkling highlights and
just about all shadow detail. You have much more latitude with color negative
film.</h5>
<h5>It didn't take me very long to realize, to both my delight and my horror,
that my digicam [a C-2020Z] behaved very much like an SLR loaded with Kodachrome. My
delight, because I was familiar with the precautions I'd have to take. Horrified
because I realized that the sensor system has no more latitude than Kodachrome,
and that I'd always have to stay on my toes. Fortunately, it doesn't cost me
anything to bracket my exposures. Hopefully, for that &quot;once in a
lifetime&quot; shot, I'll have the camera properly adjusted for the situation <i>before</i> the moment arises.</h5>
<h5>The Olympus engineers were <i>brilliant</i> when they included 1/3-stop exposure
increments in the design. We need this level of precision.</h5>

</blockquote>

<p>Tony's observations ring true in my own experience with digital
photography.&nbsp;</p>

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<hr>

<h2><a name="editor"></a><strong>Editor's Note</strong></h2>

<p>The exposure display on my digital camera has taught me a lot about exposure. I've come to consider the camera firmware a handy portable collection of
exposure tables�not the last word, mind you, but a valuable reference and usually a good place to
start. </p>

<p> Thanks to the <a href="digital.htm#freedom"> freedom to
experiment</a> and the <a href="digital.htm#feedback"> instant feedback</a> that
digital photography alone affords, I'm developing the
feel for exposure that always seemed to elude me with film, and I'm now
embarking on a fairly relaxed venture into the realm of <a href="#tonality">tonality</a>
beyond the camera's one-size-fits-all theory of exposure. </p>

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<hr>

<h2><strong><a name="rules"></a>Editorial: The Proper Role For
Rules</strong></h2>

<p><a href="./#warranty"><em><strong><img
src="underconst.gif"
alt="Marks areas under contruction--stay tuned. Click to review Limited Warranty section on the home page."
align="baseline" border="0" width="24" height="15"></strong></em></a>  Under construction...</p>

<p><img
    src="maybe.gif"
    alt="Marks content that should probably be confirmed independently.  Click to go to the corresponding article."
    border="0" width="16" height="16">&nbsp;&nbsp;Entering the soapbox zone...</p>

<blockquote>

<h5>In my experience, people who don't bother to learn the rules of photography
� those &quot;hard&quot; rules, the ones that concern focal length and
apertures and shutter speeds and composition � occasionally produce a fine
photograph. Most of the time they produce junk, and blame the camera, the film,
the lab, the subject, the weather � everything but themselves. God save me
from &quot;creative&quot; photographers who refuse to learn the basics.</h5>

  <h5>�Photographer and educator <a href="http://www.ingraham.ca/bob/index.html">Bob
  Ingraham</a>, Vancouver, BC, writing on <a href="index.htm#rpd">RPD</a></h5>

</blockquote>
<p>In this article's lead-off section <a href="#who">Who's In Charge Here?</a>,
capturing the photographer's <a href="#vision">inner vision</a> was held up as
the ultimate goal in any serious photograph. Coaxing the equipment to join you
in that vision often involves considerable craft, but without a mastery of the
rules of photography <i>and</i> their limits, the craft often comes up
short.&nbsp;</p>

<p>Bits of photographic wisdom that might come across as &quot;rules&quot; are
everywhere in this site, and particularly in this article, so let's talk for a
moment about the proper role for rules. Of the many definitions of the word <i>rule</i>
listed in the <a href="http://www.merriamwebster.com/cgi-bin/dictionary">Merriam-Webster
Collegiate Dictionary</a>, two are particularly pertinent:</p>

<ul>
  <li>
    <p style="margin-bottom: 9">&quot;a prescribed guide for conduct or
    action&quot;</li>
  <li>
    <p style="margin-bottom: 9">&quot;a usually valid generalization&quot;</li>
</ul>

<p>The latter comes a lot closer to the way good photographers use rules, but
I'd like to offer to two alternative definitions of <i>rule</i>:</p>

<ul>
  <li>
    <p style="margin-bottom: 9">a <i>trade-off</i> that usually works in a
    specific context</li>
  <li>
    <p style="margin-bottom: 9">a condensation of one or more potentially
    complex decisions that may or may not be worth rehashing at the moment</li>
</ul>
<p>I emphasize the word <i>trade-off</i> above because at bottom, all
photographic rules are trade-offs. They help you gain or avoid something,
invariably at the expense of something else likely to be less valuable under the
circumstances. Rules hit their limits when that something else ceases to be
expendable.&nbsp;</p>

<p>Taking rules beyond their limits can easily do more harm than good. To avoid
rule backfires, you must first understand exactly what's at stake, and that
comes only with study, experimentation and practice�all of which are rather
painless on the digital side. Once facile with the rules <i>and</i> their
limits, you'll be in a position to judge whether the inherent trade-offs take
you toward or away from your <a href="#vision">inner vision</a> of the scene.</p>

<hr>
<h3><a name="breaking"></a>Breaking the Rules&nbsp;</h3>

<p>Slavish devotion to rules without acknowledging their limits is asking for
trouble and seldom leads to art, but flaunting photographic rules firmly rooted
in the underlying physics is usually a recipe for disappointment if not
disaster. Ignoring the &quot;softer&quot; rules relating to composition,
lighting and the like may or may not work out in a given situation, but you have
more wiggle room there. When in doubt, go <i>beyond</i> the rules to revisit the
underlying trade-offs. With a digital camera, testing the limits has never been
easier.</p>

<p>When time or circumstance keeps you from following the rules, you get what
you get. You may end up with a real keeper, flaws and all, but more often, you
get a mess. (Many a famous photograph owes at least some of its charm to
happenstance, but such successes are hard to build on.) Not surprisingly, the
knack for judicious rule-breaking that marks a good photographer seems to come
to those most in touch with their <a href="#vision">inner vision</a> and the
spirit rather than the letter of the rules.&nbsp;</p>

<h5>Acknowledgment: Thanks to Bob Ingraham, Dave Martindale and many others for
insightful <a href="index.htm#rpd">RPD</a> posts that helped to crystallize and
refine some of the thoughts expressed here.&nbsp;</h5>

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<h2><a name="references"></a><strong>References and Links</strong></h2>

<p>(See also the <a href="index.htm#links">home page links</a>.)</p>

<p><a href="http://www.kodak.com/US/en/consumer/pictureTaking/index.shtml">Kodak
      Guide to Better Pictures</a>�an online version of the authoritative and
      comprehensive <i>Kodak Professional Photoguide</i> available in hardcopy from <a href="http://www.amazon.com/exec/obidos/ISBN=0879857986/photonetA/">amazon.com</a>.
      The online guide covers 35 mm film photography, but a lot of the
      information applies to DP as well.
 </p>

<p>Shaw, John, <i>Landscape Photography</i>, AMPHOTO, New York, 1994.</p>

<hr>

<h3>Depth of Field and Hyperfocal Technique
 </h3>

<p> <a href="http://www.collinet.freeserve.co.uk/dpinfo_html/articles/DOF/DOF%20how.htm">Depth
of Field</a>�Tony Collins'
excellent online tutorial includes a downloadable, customizable Excel-based <a href="http://www.collinet.freeserve.co.uk/dpinfo_html/articles/DOF/DOF%20Sheet.htm">interactive
DOF graph</a>.&nbsp;
 </p>

<p><a href="http://www.wrotniak.net/photo/dof/index.html">Depth of
field and your digital camera</a>�Physicist Andrzej Wrotniak's useful and well-written
piece includes DOF tables for the Oly C-30x0Z.&nbsp;
 </p>

<p><a href="http://www.nyip.com/tips/tip_hyperfocl898.html">How to Use
Hyperfocal Distance</a>�a worthwhile New York Institute of Photography
technical reference article.
 </p>

<p><a href="http://www.photo.net/photo/optics/lensTutorial.html"> Lens Tutorial</a>�David Jacobsen's
superb technical review of lenses for <a href="http://www.photo.net/">photo.net</a>
elucidates and quantifies many issues affecting
exposure.
 </p>

<hr>

<h3>Zone System
 </h3>

<p><a href="http://photography.cicada.com/zs/toc.html">Cicada's Welcome to the
Zone System</a>�Lewis Downey's thorough introduction to the rationale and
practice of Ansel Adams' zone system for tonal control.&nbsp;
 </p>

<p><a href="http://www.apogeephoto.com/mag2-6/mag2-7rh.shtml">Using the Zone
System in the Field</a>�Bob Hickman's excellent zone system tutorial with an
emphasis on pre-visualization.
 </p>

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