Can reciprocity failure be corrected adequately in post with PS?
Can reciprocity failure be corrected adequately in post with PS?
If shadow detail is not on the negative to begin with, it cannot be added later in Photoshop.
Reciprocity failure will cause insufficient exposure.
That's the main reason to: "Expose for the shadows. Develop for the highlights".
Reciprocity failure is a property of film chemistry and its lack of linear response to exposure.
Your question as stated is meaningless. The real question I think you want is, can I correct for under exposure in photoshop? The answer is, it depends on the amount. A stop or two and you may be ok, with a bit of loss in the shadows. More, and, well, it depends.
Nope. Unless you paint in the shadow detail yourself
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I agree with the other comments. If you are shooting color film, you may be able to eliminate the color cast that results from failure of the reciprocity law, but you certainly cannot pull detail if it not there.
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Reciprocity failure with black and white requires longer exposure correct? how do you determine how much longer time is needed? Is bracketing the answer?
Every film has its own reciprocity failure rate and is usually described in the film leaflet. There have been some good discussions of this here and I personally use some of the tables referenced in this thread. The truth is for exposures longer than a few minutes, it doesn't really matter! Expose until you get bored. Continued reciprocity failure at long exposures make it almost impossible to overexpose. By guess and by god works surprisingly well!
Bracketing often isn't the answer because almost by definition you're talking about a long exposure, often in early morning or late evening. By the time you make a second exposure the light will have changed so much that it's almost impossible to meaningfully bracket. Maybe with a relatively short exposure it would help but not when the exposure is measured in many minutes and at those times of day.
You can find reciprocity tables in various places, I got mine from John Sexton at one of his workshops. I'm sure there must be some on line though I don't know how good they are.
Remember that when you add exposure time for reciprocity purposes you need to reduce development time with b&w film to avoid excessive contrast. A good table will show the appropriate reduction in development time. Ideally you'd want a table made for your specific film. Mine has times for TMax films (which require less adjustment for reciprocity than other types of film) and "all others."
Brian Ellis
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PS might be able to help some. Scanners can be pretty good about pulling detail out of thin areas of the negative that would be difficult to print onto silver gelatin paper.
Long exposures cause the shadow areas to lag behind the mid-tones and highlights...there is just not enough light/energy hitting the film in the shadow areas to stimulate the silver salts at the same rates relative to the mid-tones and highlights. During long exposures, the mid-tone and highlights are exposing normally -- so it is quite possible to "over-expose" those areas of the film relative to the shadow areas when adding over-all exposure to compensate for the lack of exposure in the shadows....which is why reducing the development to hold back the highlights is recommended.
I use the failure to get increased contrast on the negative -- I give a little more exposure to bring the shadow detail in and then give the film normal or plus development to get even more density in the highlights.
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