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Wildlife and Depth of Field
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<blockquote data-quote="WayneF" data-source="post: 326454" data-attributes="member: 12496"><p>Lenses focus at ONE distance, period. Image is more blurry away from that distance.</p><p></p><p>Aside from aperture (which when smaller, directly reduces CoC to sharpen the image, less the effects of diffraction), Depth of Field is primarily about magnification (about how well we can see the blurry spot). The blur is a gradually increasing property, but we use an arbitrary CoC value to draw a sharp DOF border line (where there is no sharp line).</p><p></p><p>Wikipedia is quite good here. <a href="http://en.wikipedia.org/wiki/Depth_of_field#Factors_affecting_depth_of_field" target="_blank">Depth of field - Wikipedia, the free encyclopedia</a></p><p></p><p>Says there: DOF is determined by subject <a href="http://en.wikipedia.org/wiki/Magnification" target="_blank">magnification</a> at the film / sensor plane and the selected lens aperture or <em>f</em>-number.</p><p></p><p>Magnification is increased with a closer subject or a longer lens.</p><p></p><p>Of course, focal length obviously affects magnification, and depth of field.</p><p></p><p>But there is one very special case. If you adjust whatever you have to adjust (focal length or subject distance) so that you create the SAME image magnification (subject fills the same percentage of the frame), you will have the SAME depth of field. It is about magnification.</p><p></p><p>So, changing focal length, and then changing where you stand to equalize it, gives the same DOF. Changing only the focal length affects DOF (and magnification).</p><p></p><p>That is very different than saying focal length does not affect DOF (which is completely laughable). There are some weird notions on the internet. People tend to make up things.</p><p></p><p>The accepted formula (down below there at Wikipedia) of course includes focal length, but can be simplified to magnification (also shown there). This includes viewing magnification - a small DX sensor requires more enlargement than a larger FX sensor (DX requires smaller CoC - and typically also uses a shorter lens to show the same view). Also whether you print 4x6 or 16x20 affects enlargement (magnification). It is about magnification (about how well you can see the blur, which is there, regardless of what you do).</p><p></p><p>So, there is of course NO ONE ANSWER, as so many fail to understand. DOF charts and calculators include Circle Of Confusion (CoC), to be an adjustment for sensor size (the expected magnification). Also the charts assume a<strong> standard viewing situation</strong>, typically 8x10 print size, viewed at a 10 inch distance. But more magnification of any type will show the blurriness better. If you blindly accept the DOF chart values, without matching their described setup, of course you will get different results. And of course, the CoC which determines the chart numbers, is an arbitrary number in the first place, judged to be the visual limit we can see (at that standard viewing distance).</p></blockquote><p></p>
[QUOTE="WayneF, post: 326454, member: 12496"] Lenses focus at ONE distance, period. Image is more blurry away from that distance. Aside from aperture (which when smaller, directly reduces CoC to sharpen the image, less the effects of diffraction), Depth of Field is primarily about magnification (about how well we can see the blurry spot). The blur is a gradually increasing property, but we use an arbitrary CoC value to draw a sharp DOF border line (where there is no sharp line). Wikipedia is quite good here. [URL="http://en.wikipedia.org/wiki/Depth_of_field#Factors_affecting_depth_of_field"]Depth of field - Wikipedia, the free encyclopedia[/URL] Says there: DOF is determined by subject [URL="http://en.wikipedia.org/wiki/Magnification"]magnification[/URL] at the film / sensor plane and the selected lens aperture or [I]f[/I]-number. Magnification is increased with a closer subject or a longer lens. Of course, focal length obviously affects magnification, and depth of field. But there is one very special case. If you adjust whatever you have to adjust (focal length or subject distance) so that you create the SAME image magnification (subject fills the same percentage of the frame), you will have the SAME depth of field. It is about magnification. So, changing focal length, and then changing where you stand to equalize it, gives the same DOF. Changing only the focal length affects DOF (and magnification). That is very different than saying focal length does not affect DOF (which is completely laughable). There are some weird notions on the internet. People tend to make up things. The accepted formula (down below there at Wikipedia) of course includes focal length, but can be simplified to magnification (also shown there). This includes viewing magnification - a small DX sensor requires more enlargement than a larger FX sensor (DX requires smaller CoC - and typically also uses a shorter lens to show the same view). Also whether you print 4x6 or 16x20 affects enlargement (magnification). It is about magnification (about how well you can see the blur, which is there, regardless of what you do). So, there is of course NO ONE ANSWER, as so many fail to understand. DOF charts and calculators include Circle Of Confusion (CoC), to be an adjustment for sensor size (the expected magnification). Also the charts assume a[B] standard viewing situation[/B], typically 8x10 print size, viewed at a 10 inch distance. But more magnification of any type will show the blurriness better. If you blindly accept the DOF chart values, without matching their described setup, of course you will get different results. And of course, the CoC which determines the chart numbers, is an arbitrary number in the first place, judged to be the visual limit we can see (at that standard viewing distance). [/QUOTE]
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