Mr. Mark wrote:

Someone said in alt.photography that "film" lenses are designed to
focus the different color wavelengths differently to make up
for the layered emulsion in film. That sounds like non-sense to me.

I believe you're right.

The 'layers' of film emulsions are so thin as to escape correction in
the optics. Film thickness variance, optics variances, film transport
variances and so on, combined, are huge compared to the thin-ness of the
film emulsion.

Further, the film companies have differing emulsion build up designs,
including Fuji "4th layer" in some negative films. I never heard of
needing special lenses for that...



Opinions?

The only 'issue' I know of, and don't pay much attention to, is whether
UV filters are necessary anymore. A flat piece of optical glass as a
sacrificial filter (or better: none at all) is all that is needed. This
does apply to CCD (lower UV sensitivity than film), I don't know about CMOS.

OTOH I've seen another claim that lack of UV filtering may lead to
'blooming' when photosites are close to saturation. (May apply to CMOS
and not CCD, I don't know).

All the lenses, unless designed to filter specifically, pass a range of
light far larger than the visible range we're interested in but are
centered in the visual spectrum where focus on the film plane is
concerned. The sensors have filtering (to greater or lesser degrees) in
their covers to block IR and possibly UV.

Cheers,
Alan.

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