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Old Feb 7, 2007, 2:00 AM   #11
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Marc H wrote:
Some lenses even improve on a 1.6x crop camera.

Some lenses have small problems on the edge of the lens, but the 1.6 crop camera only uses the center part of lenses made for full frame camera's, and doesn't use the problem parts.
No that's not right. The whole of the lens is used to make the image circle. What you are disgarding with the 1.6 crop is the outer part ofthe image circle, which is of lower quality.
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Old Feb 7, 2007, 5:39 AM   #12
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kenbalbari wrote:
"Depth of field" should be mentioned because this is the other thing that changes with the crop factor. To get the same depth of field (the same region in focus), apply the crop factor also to the f-stop. Since the light gathering ability doesn't change, you would also need to adjust either the lighting, or the ISO. Thus, suppose you have a shot, on a "full frame" 35mm camera, at 80mm, f8, ISO 200. Without changing the light, or subject distance, you would get the same exact photo on a 1.6 crop factor camera by shooting it at 50mm, f5.0, ISO 80.
I agree, except that it would be more likely that someone would adjust the exposure by adjusting the shutter speed, not the ISO. I know of cameras with autoexposure modes of Shutter Priority and Aperature Priority, but I don't know of any that has an ISO Priority.

Thus, with 'a shot, on a "full frame" 35mm camera, at 80mm, f8, ISO 200' at 1/30th of a second, you would get 'the same exact photo on a 1.6 crop factor camera by shooting it at 50mm, f5.0,' ISO 200 at 1/125th of a second (barring subject movement and camera shake.)

But this is all academic anyway, since hopkinsgdoesn't have a 35mm SLR. And while some of the reference material hopkinsghas access to (and will continue to have access to) refers to what focal lengths (in absolute terms)are best for what kinds of photography (hopkinsg: I have read several times that 85mm or 100mm are the best focal lengths for portrait photography.), he is only likely to come across references to f-stops in relative terms. That is, there are probably more references like "A larger f-stop (a smaller aperature) results in a greater depth of field", not "An f-stop of f8.0 provides the best depth of field for this kind of photography."

After all, given the freedom provided by autoexposure, the choice of one f-stop over another is more artistic than technical, unlike focal length. If hopkinsgshows up at someones home with a100mm lens to take their portrait, then hopkinsgand the subjectwill likely have to be in different rooms (which is a technical problem). But hopkinsgwill always be able to select from any available aperature (based on artistic inclination.)
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