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Photography Q&A
Does standing further back & zooming in increase the acceptable focus zone?
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<blockquote data-quote="WayneF" data-source="post: 550785" data-attributes="member: 12496"><p>That which you call focus is called Depth of Field (the distance zone in which the scene appears sharp to us). Narrow Aperture does increase DOF, as does shorter focal length, greater focus distance, or smaller camera sensor. These last three each alone all cause a smaller subject image. It appears sharper because it is a wider view, and thus shows smaller objects (if seen at the same enlargement), so we can't actually see the blur. Enlarge it more and we see more.</p><p></p><p>It is Not rocket science. If you show the image objects smaller, you cannot see the blur as well, and will imagine it is sharper. But enlarge it more, then the opposite.</p><p></p><p>In any picture, focus has only ONE value, focus is at only one distance, period. But scenes have more depth, both behind and in front of this point of focus. All those other distances are simply NOT in focus. There is only one point of focus.</p><p></p><p>But the photo may or may not still look acceptable "focus". </p><p></p><p>A star seen in a telescope is a point source, it has no actual diameter seen. If we assume imaginary point sources in our photo, tiny dimensionless points, being not in focus makes that infinitesimal point appear larger, seen as an unfocused blob, but larger. This visible blob diameter seen in the lens can be computed, and is called Circle Of Confusion (CoC, see Wikipedia). </p><p></p><p>Given a specified degree of viewing magnification (standard viewing for DOF is assumed to be an 8x10 inch print viewed at 10 inches), then too-small CoC cannot be seen as blobs (seen still as a point). But larger CoC we can see as a blurred image, not sharp. What our human eye can see there is judged to be a limit for CoC (again, enlarge it more, and we can see more).</p><p></p><p>Then Depth of Field (DOF) computes the zone or distance range that will compute the CoC large enough to be visible (at the standard viewing magnification), and we call that distance range zone DOF. Scene parts within that DOF zone are imagined sharp, and those outside it are seen as blurred. It is relative however, and a very gradual change with distance. There is still only one distance in focus, and areas slightly outside or slightly inside this DOF zone are hardly different.</p><p></p><p>DOF calculations are simply a mathematical limit of the numbers. Saying for example, if our CoC limit is 0.03 mm, then 0.02999 is inside it, and 0.03001 is outside of it, but there is no actual visible difference between them at that point. But DOF draws a line there (assuming the standard viewing magnification). And certainly 0.01 is much better, and 0.05 is much worse.</p><p></p><p>So regarding DOF, definitions of CoC diameter that our eye can see is just someones supposed judgement call (100 years ago), and our actual viewing enlargement is always arbitrary too, so we ought NOT to expect exact numbers from DOF. But it is a good guide. The concept is much more valuable than any specific numbers from it. We certainly should know how to increase or decrease it (and position it), as desired.</p><p> </p><p>If you want some point to be very sharp, then focus there (like the eye in a portrait). If you want a larger range to be pretty much sharp, almost, then you might place focus at some compromise distance to enhance the full range of interest.</p><p></p><p>See Wikiipedia</p><p></p><p>Circle of Confusion</p><p></p><p>Depth of Field.</p></blockquote><p></p>
[QUOTE="WayneF, post: 550785, member: 12496"] That which you call focus is called Depth of Field (the distance zone in which the scene appears sharp to us). Narrow Aperture does increase DOF, as does shorter focal length, greater focus distance, or smaller camera sensor. These last three each alone all cause a smaller subject image. It appears sharper because it is a wider view, and thus shows smaller objects (if seen at the same enlargement), so we can't actually see the blur. Enlarge it more and we see more. It is Not rocket science. If you show the image objects smaller, you cannot see the blur as well, and will imagine it is sharper. But enlarge it more, then the opposite. In any picture, focus has only ONE value, focus is at only one distance, period. But scenes have more depth, both behind and in front of this point of focus. All those other distances are simply NOT in focus. There is only one point of focus. But the photo may or may not still look acceptable "focus". A star seen in a telescope is a point source, it has no actual diameter seen. If we assume imaginary point sources in our photo, tiny dimensionless points, being not in focus makes that infinitesimal point appear larger, seen as an unfocused blob, but larger. This visible blob diameter seen in the lens can be computed, and is called Circle Of Confusion (CoC, see Wikipedia). Given a specified degree of viewing magnification (standard viewing for DOF is assumed to be an 8x10 inch print viewed at 10 inches), then too-small CoC cannot be seen as blobs (seen still as a point). But larger CoC we can see as a blurred image, not sharp. What our human eye can see there is judged to be a limit for CoC (again, enlarge it more, and we can see more). Then Depth of Field (DOF) computes the zone or distance range that will compute the CoC large enough to be visible (at the standard viewing magnification), and we call that distance range zone DOF. Scene parts within that DOF zone are imagined sharp, and those outside it are seen as blurred. It is relative however, and a very gradual change with distance. There is still only one distance in focus, and areas slightly outside or slightly inside this DOF zone are hardly different. DOF calculations are simply a mathematical limit of the numbers. Saying for example, if our CoC limit is 0.03 mm, then 0.02999 is inside it, and 0.03001 is outside of it, but there is no actual visible difference between them at that point. But DOF draws a line there (assuming the standard viewing magnification). And certainly 0.01 is much better, and 0.05 is much worse. So regarding DOF, definitions of CoC diameter that our eye can see is just someones supposed judgement call (100 years ago), and our actual viewing enlargement is always arbitrary too, so we ought NOT to expect exact numbers from DOF. But it is a good guide. The concept is much more valuable than any specific numbers from it. We certainly should know how to increase or decrease it (and position it), as desired. If you want some point to be very sharp, then focus there (like the eye in a portrait). If you want a larger range to be pretty much sharp, almost, then you might place focus at some compromise distance to enhance the full range of interest. See Wikiipedia Circle of Confusion Depth of Field. [/QUOTE]
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Photography Q&A
Does standing further back & zooming in increase the acceptable focus zone?
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