Paper has 2 kinds of reciprocity failure, speed and contrast.
In speed reciprocity failure, the paper loses speed with exposures much above about 1 minute and it gains speed below about 1 second.
In contrast reciprocity failure, contrast goes down with longer exposure and up with shorter exposure.
These effects vary vastly among papers, but can be disastrous with VC papers where you are trying to design matched reciprocity failure between 2 emulsions.
Some papers have virtually no reciprocity failure, others have a lot. Some papers for example, are designed to work in different ranges. Digital papers are designed to work with high intensity short exposures and if you use them on-easel, they will respond differently than the mfgrs. data sheet.
Historically, Kodak made 2 ranges of papers. One for high intensity short exposures and one for low intensity long exposure.
MattKing pointed out the paper intended for electronic exposure may be susceptible to reciprocity failure. You probably won't encounter that paper. I was thinking of getting some, so it might pertain to me one day.
If I understand, with an Omega 4x5 enlarger and normal paper, you will not encounter reciprocity failure. Even if you did, the practice of making test strips completely negates the impact - because you would be testing the actual results you get for the actual times you expose.
As mentioned, don't stop your lens down to f/22. Use f/8, +/- a stop if necessary and none of this will be an issue..
You can run into it between 1' and 10".
Originally Posted by Photo Engineer
For clarity, do you mean with times between 10 seconds and 60 seconds (1 minute)?
Yes, sorry, 1" and 10". Kodak made papers for photo labs with the aim centered at 1' or shorter and another range of papers for enlarging with the aim centered at 10" and above. We used to run 2 tests on each emulsion or coating to see which range it would be most suitable for. We also used to base experiments on these two ranges.
Usually the one paper was sold in narrow rolls and the other was sold in sheets or wide rolls.
In the case of color, the curves were adjusted slightly to favor neutral for the narrow paper, and slightly pink for the wide and cut sheet. The latter was to make flesh tones and whites more appealing, as the majority of prints were of weddings or were portraits.
Reciprocity failure was critical in this case as color could shift.
Brian - you're assuming that everyone else's enlarger is the same as yours, whereas enlarger light
sources vary dramatically in terms of light output, just as different papers have different effective
speeds, which is complicated in the case of VC papers. Color enlarging can present distinct recip
challenges, depending on what you are specifically doing. Current RA4 papers are generally cooperative because they tend to print quickly on most colorheads. Although current Crystal Archive
options are used in laser systems, they balance just fine in ordinary optical printing - they're deliberately engineered dual-usage.
I assumed black and white paper, where using a test strip would completely mitigate contrast or speed changes due to reciprocity law failure... Because it provides a proof of actual results.
For color printing I recommend avoiding reciprocity failure by exposing for approximately the time the paper is optimized for.
yes, making a test strip under actual conditions is the best idea!The math gets you close but not necessarily on target.