>... and now that I have your attention again (we previously
>discussed my AI-non-S 28mm): can you comment on the
>'image clarity' discussions that have been going on for a
>while. When I was a young photographer, I learned about
>the 2-3 stops or f/8 rules (which you already commented
>on elsewhere) to compensate for lens abberations -- but today,
>many claim that top-grade lenses (Nikkors...) really perform at
>or near diffraction limits with the _film_ as the limiting
>factor at wide apertures (apparently due to dispersion
>in the film planes), hence leading to the f/8 rule.
>
>I get the point about measuring using aerial imaging for lenses,
>but I'd like to see a good explanation for the film dispersion
>phenomena (or whatever it is).
>
>Do you have any input/references/hints? I thought I'd ask
>someone with a proper amount of insight here (that was
>another compliment ;-)
>Cheers,
>-- Per. [peb@pine.dk (Per Baekgaard)]

Hmmm, sorry, no help here...
Many good Nikkors clearly improve in the edges and corners
more with stopping down than they do in the center...
All Nikkors improve in the center with stopping down to
at least f4...
Virtually all Nikkors peak in the center around f8 (a few
peak sooner)...
Some superwides, PC's, and zooms require considerable
stopping down to peak the corner performance...
Some superwides perform better in the corners with color
filters in B&W, or with color film instead of B&W...
Using sharper film generally improves performance...
Which doesn't address the film-dispersion question at
wide apertures, but I do have some doubts about the
importance of this (I once had a 50mm f1.4 Nikkor that
wasn't very good on the edges, but the center was really
excellent at f2.8, and it peaked around f4 [even looked
good on a 3X converter in the center...])...
Dunno...