CN writes:
<<What Roger is actually saying is that resolution of 610 looks pretty good
compared to 325 wide open. You have to close down 3 stops to f/4 to even equal
the f/16 result. What his results do show is that <<diffraction has a very real
effect and starts taking its toll about where theory says it should.
Yes, agree with you on everything to a point. Roger also demonstrated that the
MTF decline by stopping down an extra stop was quite modest and that he would
stop down more even to F16 for some landscapes.
It clearly depends on the image and the importance of critical sharpness at
different distances. Recall from Merklinger's article that by focusing at
infinity one gains 6 fold increase in resolution for distant objects and only
loses 2X at the near limit of DOF.
http://www.trenholm.org/hmmerk/TIAOOFe.pdf (about page 32)
One easy solution, if circumstances permit, is to focus stack at a wider
aperture and eliminate the compromise (but introducing others).
Now I know it is really mid-winter with a diffraction/dof thread, Mike
--
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