From: Joachim Oppenheimer (joachim@microdsi.net)
Date: 06/04/02-11:25:28 AM Z
As a sometimes-pinhole photographer I am aware that films differ in their
response to reciprocity failure at least at the lower part of the curve. It
is paradoxical that conventionally "Slower" TMAX-100 is "Faster" than
TMAX400, if one looks at Kodak's data sheets. Underdevelopment removes
silver halide uniformly from a piece of film so that a fixed percentage
removal, say 10%, will have little noticeable effect in an area of silver
halide deposition that is loaded with the silver salt but a proportionately
greater effect in the thinner areas - 10% of an arbitrary one picogram
silver halide leaves 0.9 picogram but 10% of 100 picograms still leaves 90.0
picograms. I think the guide directing you in the opposite direction is
incorrect. Joachim
> -----Original Message-----
> From: Sandy King [mailto:sanking@clemson.edu]
> Sent: Tuesday, June 04, 2002 12:49 PM
> To: alt-photo-process-l@sask.usask.ca
> Subject: Re: long exposures, reciprocity failure and development times
>
>
>
> Shannon,
>
> Specific films may differ but as a general observation an increase in
> exposure time to adjust for reciprocity failure needs to be
> accompanied by a decrease in time of development to avoid too much
> contrast. Good data sheets will generally suggest how much to cut
> development depending on the amount of reciprocity adjustment.
>
> I am not familiar with the requirements of poinhole photography with
> regards to long exposures.
>
> Sandy King
>
>
>
>
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>
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> > I have a chart that shows reciprocity failure adjustments for various
> >black and white films. This chart also suggests decreasing development
> >times as exposure times increase. The reasoning is that
> reciprocity failure
> >affects the shadow areas more than the highlight areas. Is this
> correct? I
> >also have a pinhole time calculator that suggests INCREASING development
> >times as exposure times increase. Which is correct? (Excuse the
> >cross-posting if you read alt-photo-process and pinhole-discussion.)
> >
> >--shannon
>
>
> --
>
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