The reciprocity effect is only important for exposures of several minutes. For normal applications it can be ignored. When recording diffraction patterns on an optical bench for example, where exposures may be as long as fifteen minutes, the effect becomes serious. But in this case the film and illumination is not the same as that encountered in ordinary photography - and there are other factors.
My recent experiment would indicate that a one stop push is a one stop push and a two stop push is two - for practical purposes. I don't have a densitometer - as I said before - and I cannot say with any certainty what the actual change in density and contrast was. I can only suggest that people take a look at the results: http://personal.inet.fi/cool/don.williams/hold/index.htm Don Dr E D F Williams http://personal.inet.fi/cool/don.williams Author's Web Site and Photo Gallery Updated: March 30, 2002 ----- Original Message ----- From: "Joseph McAllister" <[EMAIL PROTECTED]> To: "PDML" <[EMAIL PROTECTED]> Sent: Wednesday, July 24, 2002 1:04 AM Subject: Re: Push Processing Film > on 07/23/02 13:43, [EMAIL PROTECTED] shared with me: > > > In a message dated 7/23/2002 12:28:43 PM Pacific Daylight Time, > > [EMAIL PROTECTED] writes: > > > > > >> It's been mentioned before that 100 ISO film pushed 1 stop should be shot > >> at 320 ISO and that shooting it at 200 ISO is not a 1 stop push. How valid > >> > >> is this? > > > > A doubling of film speed is a one stop push. Rating ISO 100 film at ISO 200 > > is a one stop push, at ISO 400 it's a two stop push. This is the way I've > > always understood it. > > > > I found this, however, on the Kodak web site: > > > > "With longer development times, such as those used in push processing, EI > > values actually do increase, but only slightly. Underexpose a film by two > > stops and give it a two-stop push, and the real film speed will typically > > increase by perhaps a half stop. This means that the film is really > > underexposed by only 1 � stops, not two stops. But it is underexposed. " > > > > So, rating ISO 100 speed film at ISO 400 is only a 1 1/2 stop under exposure. > > Hummm.... > > Making an assumption, I'd say that the push processing of film is akin to > long exposures. The longer you expose a film, the longer you must actually > expose it to get the exposure you were aiming for. I don't remember the > phrase for this, but it means if you expose film x for one minute, to > achieve what any exposure chart will calculate for you, you must really > expose for 1.5 minutes. Other films will need other adjustments (is it > Reciprocity Failure?) based on their inherent exposure properties. Sometimes > wrongly confused with developer exhaustion. > > JoMac, Pentaxian > "Pentax, Quadraphonic, Betamax, Macintosh" > > and above the rest. > k t, > s e n > Living life a w o > almost parallel to, r > yet ever so slightly o u t -------> f > - > This message is from the Pentax-Discuss Mail List. To unsubscribe, > go to http://www.pdml.net and follow the directions. Don't forget to > visit the Pentax Users' Gallery at http://pug.komkon.org . - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
