Reciprocity failure question...

[Carterofmars]

Can reciprocity failure be corrected adequately in post with PS?

[Gem Singer]

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".

[chuck94022]

Can reciprocity failure be corrected adequately in post with PS?

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.

[Andrew O'Neill]

Nope. Unless you paint in the shadow detail yourself

[E. von Hoegh]

Can reciprocity failure be corrected adequately in post with PS?

No.

[Preston]

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.

--P

[Carterofmars]

Reciprocity failure with black and white requires longer exposure correct? how do you determine how much longer time is needed? Is bracketing the answer?

[mitomac]

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!

[Brian Ellis]

Reciprocity failure with black and white requires longer exposure correct? how do you determine how much longer time is needed? Is bracketing the answer?

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."

[Heroique]

Reciprocity failure with black and white requires longer exposure correct?

How do you determine how much longer time is needed?

Here’s a general “starter’s chart” for times under 2 minutes for traditional b/w films (not T-grain), until one becomes more familiar w/ personal equipment & film, darkroom processing habits (such as “N-1” or “N-2”), and preferred results. As you learn more, adjust to your taste:

• Metered 2 sec. – use 4 sec (2x)
• 4 sec – use 12 sec (3x)
• 8 sec – use 32 sec (4x)
• 15 sec – use 75 sec (5x)
• 30 sec – use 3 min (6x)
• 60 sec – use 7 min (7x)
• 120 sec – use 16 min (8x)

Over time, my personal reciprocity charts for various films depart more and more from the chart above, and from manufacturing suggestions, but not by a very significant amount.

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Side note:
“This is commonly known as ‘failure of the reciprocity law’,” AA says in his book, The Negative, “but I prefer the term reciprocity effect as it is not actually a ‘failure.’ ”