Hi Doug:
<< A simple focal length/4 formula that is often given is just as effective
for photography. In this case 90/4 yields f/22 as the minimum stop to prevent
image loss from diffraction. >>
Thanks Doug. That must have been what L.A. Mannheim used in The Olympus OM
Way - the source of my information (see Close-up Depth of Field table in the
Facts and Figures appendix). I detect no difference under a loupe between the
diffraction limited aperture and either one stop smaller or larger. But then
I'm looking at 3-D flower shots in which much of the subject matter lies
within the circle of confusion - hence is already less sharp than optimum. I
haven't done high resolution 2-D copy work in a long-time, but I would suspect
that a difference could be detected there. But in 2-D it wouldn't matter
since the optimum aperture is about 2-3 stops from wide open.
John Shaw is using zooms for macro work? Yikes, he must have got lazy.
Gary Reese
Las Vegas, NV
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