Dr. Focus fleshes out some of the experimental design difficulties.
It is likely much easier to slightly move the cam on a geared head or
geared
focusing rail then play with the the focusing helicoid. Suspect the
tiny change in lens to subject distance won't
matter much if the test is designed properly. DXO does this to ensure
optimized focus (they had difficulty with that a few years back)
http://www.dxomark.com/index.php/About/In-depth-measurements/DxOMark-testing-protocols/MTF
The previous version of this page was more descriptive. They take many
images and calculate their "Blur Index" at several apertures and use
the best
as the one with the optimized focus. (some Zeiss lenses can get
hammered at some focusing distances due to purposely left field
curvature--doesn't make them an "inferior" for many purposes however)
Cognisys Stack shot automated focusing rail for focus stacking claims a
precision down to 0.01mm if desired when moving the cam.
Iterations are your friend to average out the focusing differences,
Bottom line, I still think AG's conjecture that there may be a
discernable dof or distribution of dof difference between the two
lenses is a testable hypothesis w/o making it into a Ph.D. thesis.
There is commercial software where one inputs the lens elements,
spacing etc and it will provide ray traces and computation of
aberrations.
I am not aware that it does full wave dof calculation though Zeiss
clearly has the software.
http://skyscientific.com/
AG is a superb engineer, he'll figure it out.
Mike
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