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Re: a lot of over-exposed negatives: what to do?

At 05:28 PM 04/16/2001 -0500, you wrote:
>on 4/16/01 5:02 PM, shannon stoney at sstoney@pdq.net wrote:
>
>> alt-process, and I have come to the conclusion that most of the negatives I
>> made over the past year are over-exposed for those processes.  That is, I
>> thought my film speed was 320 for alt-process as for silver,  and it's
>> probably really closer to 400.  So, all the shadow areas are over-exposed.
>> But I would like to salvage these negatives if I could
>
>"Salvage" !? What are you talking about? Between 320 asa and 400 asa? taking
>in account the variations due to metering, accuracy of the shutter speed,
>etc... your shadows, if over-exposed, would be over-exposed by a 1/4 of a
>stop or so. 
>/ln
>-- 
>mailto:luc@overland.net
>http://www.sotolgallery.com
>
  FWIW, the ISO standard includes a 1.25X safety factor so ISO-320 film is
really 400 speed if you actually measure the speed point. this difference
is small. Film has a tremendous OVERexposure latitude and nearly NO UNDER
esposure latitude. On the overexposure side the latitude is several stops.
Minimum exposures consistent with good shadow detail are considered
desirable since grain and loss of sharpness due to scattering of light in
the emulsion are minimized. However, over a range of six to ten stops it is
nearly impossible to tell any difference in carefully made prints.
  Development controlls contrast. Its quite possible to have an overexposed
but flat negative. Actually, that is what Zone System contraction is all
about. Over development combined with normal exposure results in rather
high highlight densities. Some alternative printing methods require higher
contrast negagives than conventional printing because the exposed areas
become somewhat desensitized. So, in order to get adequate densities in
them overall exposure must increased. This will result in grayed down
highlights unless the negative is contrasty enough to keep the highlights
clear. 
  Over exposure will result in negatives which are a little (or maybe a
lot) dense overall, but the contrast will be normal. They will print
normally except for requiring longer exposure times. "Normal" exposure for
ISO rated materials is anywhere from the ISO speed to about two stops more,
depending on the developer and nature of the scene being recorded. A great
many photographers prefer to rate film at about half its ISO speed because
they get better shadow rendition that way. 
  Since the response of film is exponential a 20% difference in exposure,
especially toward the high side, is probably not visible or of practical
importance. 
----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com