"film" and "digital" lenses
 

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.

Opinions?

--
Mark

Photos, Ideas & Opinions
http://www.marklauter.com

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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-- e-meil: Remove FreeLunch.

"Alan Browne" wrote in message
...
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...

Or special lenses for black and white...

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.

Opinions?



I heard there is a coating on the rear element to prevent reflections
off the sensor for digital lenses though I've not seen any example of
these reflections so I assume it's quite a minor issue.


--
Paul Furman
http://www.edgehill.net/1
san francisco native plants

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.

Thats BS..

--

Stacey

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.

Like George Preddy claiming Lateral Chromatic Aberration was a Sigma
feature...

Martin Francis wrote:

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...


Or special lenses for black and white...

Good point.

Cheers,
Alan



--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
-- [SI] gallery & rulz: http://www.pbase.com/shootin
-- e-meil: Remove FreeLunch.

Paul Furman wrote:

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.

Opinions?




I heard there is a coating on the rear element to prevent reflections
off the sensor for digital lenses though I've not seen any example of
these reflections so I assume it's quite a minor issue.

So minor that DSLR's cannot do OTF TTL metering. Any need for coatings
to help in this regard sounds like the cry of the marketeers.

Cheers,
Alan.


--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
-- [SI] gallery & rulz: http://www.pbase.com/shootin
-- e-meil: Remove FreeLunch.

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...

Or special lenses for black and white...

That was the first thing I considered. I even asked the poster about that
and several folks have replied that he's full of $#@!, but he has apparently
disappeared.

--
Mark

Photos, Ideas & Opinions
http://www.marklauter.com

I heard there is a coating on the rear element to prevent reflections
off the sensor for digital lenses though I've not seen any example of
these reflections so I assume it's quite a minor issue.

Wouldn't film do the same thing? It's shiny plasticy stuff after all.

--
Mark

Photos, Ideas & Opinions
http://www.marklauter.com