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#1
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Reciprocity
In the past reciprocity has been a concern when processing films if the
chemicals and water vary too much in temperature. Is this still true with modern b/w film emulsions? |
#2
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Reciprocity
I am not sure what you mean by reciprocity. In photography this term
usually refers to reciprocity law failure, that is, that while the total light energy should result in the same exposure in practice the time of exposure or intensity does make a difference. Very long and very short exposures do not have the same effect as a medium speed exposure. This effect is a characteristic of the emulsion and is not affected by the developer or temperature. Now, if you are refering to the rate at which development varies with temperature, there is certainly variation. It is partly due to the developer and partly the film. For one thing some developing agents change activity faster with temperature than others. Also, the pH of the developer has an effect on the above. At low temperatures for instance, Hydroquinone tends to become inactive. This effect depends on pH. The effect is most apparent in normal film and print developers of medium pH. In very high pH developer such as high contrast or lith developer, Hydroquinone stays active at low temperatures. Kodak and other developer manufacturers, have charts showing the rate at which developers change activity. I hope one of these addresses your question. -- Richard Knoppow |
#4
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Reciprocity
"Blaine Owens" wrote
In the past reciprocity has been a concern when processing films if the chemicals and water vary too much in temperature. Is this still true with modern b/w film emulsions? I think you may mean 'reticulation': the emulsion crinkles and the resulting picture looks a bit mosaic-like. Not as big an issue as it was with modern films. Still an issue, though. Keep all chemicals & water within a few degrees of each other. Before reticulation there is grain clumping -- something else to be avoided. Some photographers reticulate for arty-farty effects, Mortenson comes to mind. Hot developer is the easiest way to cause the problem, possibly an antique film - Efke & Co. - would help. -- Nicholas O. Lindan, Cleveland, Ohio Consulting Engineer: Electronics, Photonics, Informatics. Remove blanks to reply: n o lindan at ix . netcom . com |
#5
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Reciprocity
Reciprocity, (or more properly reciprocity departure) usual usage is for a
non-linear relationship between illumination and exposure in films at slower speeds. In other words one second at f/5.6 no longer equals 4 seconds at f/11 but the longer exposure instead might be 2 to 4 times more exposure. There is also a non-linear relationship between developed density and time/temp once you get outside the range of approximately 60-80 degrees F, this is not normally called reciprocity. And another term you may have come across, reticulation, caused by emulsions cracking or moving off the base due to high processing temperatures outside the manufacturer's recommended range. -- darkroommike "Blaine Owens" wrote in message ... In the past reciprocity has been a concern when processing films if the chemicals and water vary too much in temperature. Is this still true with modern b/w film emulsions? |
#6
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Reciprocity
HI,
Is there a general standard reciprocity chart or is there a different one for each film? Cheers, Bogdan Mike King wrote: Reciprocity, (or more properly reciprocity departure) usual usage is for a non-linear relationship between illumination and exposure in films at slower speeds. In other words one second at f/5.6 no longer equals 4 seconds at f/11 but the longer exposure instead might be 2 to 4 times more exposure. There is also a non-linear relationship between developed density and time/temp once you get outside the range of approximately 60-80 degrees F, this is not normally called reciprocity. And another term you may have come across, reticulation, caused by emulsions cracking or moving off the base due to high processing temperatures outside the manufacturer's recommended range. -- __________________________________________________ ________________ Bogdan Karasek Montral, Qubec e-mail: Canada "Wovon man nicht sprechen kann, darber muss man schweigen" "What we cannot speak about we must pass over in silence" Ludwig Wittgenstein __________________________________________________ ______________ |
#7
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Reciprocity
You can make generalizations but each film is different, classic example:
TMax 100 has "better" reciprocity than TMax 400 and exposure compensation will be shorter than with the normally higher speed film. Most film makers publish reciprocity charts see for example: http://www.kodak.com/global/en/profe...shortexposures Easy enough to GOOGLE for the charts. -- darkroommike "Bogdan Karasek" wrote in message ... HI, Is there a general standard reciprocity chart or is there a different one for each film? Cheers, Bogdan Mike King wrote: Reciprocity, (or more properly reciprocity departure) usual usage is for a non-linear relationship between illumination and exposure in films at slower speeds. In other words one second at f/5.6 no longer equals 4 seconds at f/11 but the longer exposure instead might be 2 to 4 times more exposure. There is also a non-linear relationship between developed density and time/temp once you get outside the range of approximately 60-80 degrees F, this is not normally called reciprocity. And another term you may have come across, reticulation, caused by emulsions cracking or moving off the base due to high processing temperatures outside the manufacturer's recommended range. -- __________________________________________________ ________________ Bogdan Karasek Montral, Qubec e-mail: Canada "Wovon man nicht sprechen kann, darber muss man schweigen" "What we cannot speak about we must pass over in silence" Ludwig Wittgenstein __________________________________________________ ______________ |
#8
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Reciprocity
"Rod Smith" wrote in message ... In article , (Blaine Owens) writes: In the past reciprocity has been a concern when processing films if the chemicals and water vary too much in temperature. Is this still true with modern b/w film emulsions? I suspect you're thinking of reticulation, not reciprocity. Snipping... I think you are right. Also a good answer:-) -- --- Richard Knoppow Los Angeles, CA, USA |
#9
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Reciprocity
"Bogdan Karasek" wrote in message ... HI, Is there a general standard reciprocity chart or is there a different one for each film? Cheers, Bogdan Each one is different. Most manufacturers publish reciprocity curves for both films and papers. Reciprocity failure can cause not only exposure errors but color shifts in color materials where the differenct layers reacact differently. Kodak has a data sheet listing reciprocity characteristics for its materials. Search their web site for either reciprocity or E-31. http://www.kodak.com Modern tabular grain films, like Kodak T-Max and Fuji Acros, have much better reciprocity characteristics than older films. -- --- Richard Knoppow Los Angeles, CA, USA |
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