Hi P.J.:
As already mentioned, you seem to be exceeding the diffraction limited
aperture. The greater the magnification, the less you can stop down.
For example, by about 12x magnification, you can't stop down past f/2
without image deterioration due to diffraction. At 1:1 I believe it is
f/11
The formulas to calculate this for a given circle of diffusion
(unsharpness limit) have been posted to the List often. There are also
tables in the back of "The Olympus OM Way."
Gary Reese
Las Vegas, NV
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