In conjunction with these parameters, absolute values for DOF are defined
by the largest acceptable "circle of confusion" on the resulting image.
The general accepted standard for 35mm is 0.03mm, however some others (Carl
Zeiss and Sinar) have used 0.025mm, and there has been debate about some
manufacturers using larger standards for marking DOF on their lenses.
The question this has brought to mind: What circle of confusion diameter
does (did) Olympus use for marking DOF with the Zuiko lenses?
=================
The process of setting the DOF by using the DOF scales on the lens
is not such a high precision operation that the difference between
0.03mm and 0.025mm is all that significant, imho. Moreover, how small
the circle of confusion needs to be depends on how large you plan to
enlarge the image. Since I always prefer to have the freedom to
enlarge as much as possible (whether or not I ever do) I generally
work scenes with high DOF demands in 35mm by setting the DOF using the
scales, then stopping down 1 more stop (for smaller CoF's) as long as
that won't set the f-stop to f/22. If I can't get the DOF I need
at f/16, I might considering using f/22, particularly for some macro
shots, but most of my images on tripod are taken in the f/8 to f/16
range.
Joseph
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