Originally Posted by
Corran
I think the problem with DOF calculations, especially when using pure math to make them, is that it supposes the whole depth of focus area will be the same sharpness.
Regardless of aperture, only one point in space is "in-focus" while the rest inside the DOF is supposedly "close enough." I've found DOF calculators or DOF markings on small-format lenses to often grossly underestimate the acceptable DOF in most situations (35mm lenses especially, as they usually suppose a 4x6 "jumbo print" IIRC). If a given focus point calculates to have everything in focus front-to-back, I would stop down an additional 1-2 stops to ensure this if working at the extremes, regardless of "diffraction."
I also tend to reject the "1/3 in front, 2/3 behind" focus paradigm in many situations, especially with a strong foreground element. A foreground element inside the DOF and math claims should be "acceptably sharp" to me often seems unacceptably fuzzy on the negative - so focusing a bit closer and stopping down a bit more seems more effective. YMMV.
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