Another comment:
Popular Photography was giving at least B+ grades at f/16 in their SQF
testing . See their results, which I posted along side mine for the
35-70mm f/3.5~4.5 and 35-80mm f/2.8 Zuikos.
Theoretically the image should deteriorate after the optimum aperture.
But, we just don't detect it till it reaches a threshold deterioration.
For pure resolution, that threshold is taken to be 5 l/mm.
I was also factoring in contrast to my SQF grading. That typically
deteriorated at f/16 or f/22, with f/32 and wide open results often
quite a bit lower. The best lenses showed little difference across
their aperture range.
To choose a methodology that shows detectable deterioration after
optimum aperture requires a remarkable film and probably a larger
reproduction size. It wouldn't do me any good to evaluate the old
slides at 100X, since the film was the limiting factor.
Gary Reese
Las Vegas, NV
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