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Shouldn't DOF be exactly the same for the same actual (as opposed to 'equivalent') focal length and aperture (and 'circle of confusion' used, which is somewhat arbitrary)?


As I read that Luminous Landscape article, it's all about the circle of confusion. For yee olde 35mm film camera, the assumed circle of confusion is pretty big, corresponding to resolving 30 lines/mm. So, the DOF marks tell you how much DOF you'll get with a 30 line/mm resolution. If you're into using one of the high-end high-resolution low-speed films, as I now (vaguely) understand it, you'll have to trade off DOF for extra sharpness. That is, you'll get perfect sharpness for objects that are exactly at the focal distance, but by the time those objects are at the DOF markers, they'll be too fuzzy for your sharpness requirements.

Along those same lines, the assumption of the DOF calculator (for what it's worth), seems to be that the higher resolution (in lines/mm) of a modern D-SLR necessitates less DOF. Or, another way of of saying it, is that the higher-resolution sensor on a D-SLR is like using higher-resolution film, and necessitates a smaller circle of confusion.

I almost think I'm understanding this now...