There was a post in my thread on building my own color enlarging head that gave what the poster called "purported" spectral curves for Kodak Endura color printing paper.
Looking at those curves, I was reminded that I've heard conflicting information about color darkrooms: that they need to be totally dark (which would make sense, since the print paper is sensitive to all colors) or that there is in fact a safelight for RA-4 print papers (which, based on the curve given in that post, ought to be at appr. 575 nm, a little redder than the yellow sodium line)
What I note, however, is that the "log sensitivity" at that lowest point, the crossover between magenta-forming and cyan-forming layers, is only about -3 from the peak of the magenta-forming layer's sensitivity, and much less different from the cyan-forming peak.
This seems to me to suggest that either I don't know how to read the units they're using (a very real possibility, if they don't read like dB), or there's only about one stop less sensitivity at this minimum than there is at the paper's maximum, which would imply that the safelight, besides needed a very narrow emission spectrum, would also have to be quite dim.
Dim is okay -- anything is better than total darkness, when your eyes will routinely lose some of their adaptation from the bright image cast by the enlarger, and all that's really needed is some way to confirm the emulsion side of the paper without leaving fingerprints, and to be sure the paper is correctly aligned in the easel and submerged in the chemical trays.
But I distinctly recall being told by a friend who had done RA-4 printing that the darkroom wasn't all that dark.
Which is it?
Looking at those curves, I was reminded that I've heard conflicting information about color darkrooms: that they need to be totally dark (which would make sense, since the print paper is sensitive to all colors) or that there is in fact a safelight for RA-4 print papers (which, based on the curve given in that post, ought to be at appr. 575 nm, a little redder than the yellow sodium line)
What I note, however, is that the "log sensitivity" at that lowest point, the crossover between magenta-forming and cyan-forming layers, is only about -3 from the peak of the magenta-forming layer's sensitivity, and much less different from the cyan-forming peak.
This seems to me to suggest that either I don't know how to read the units they're using (a very real possibility, if they don't read like dB), or there's only about one stop less sensitivity at this minimum than there is at the paper's maximum, which would imply that the safelight, besides needed a very narrow emission spectrum, would also have to be quite dim.
Dim is okay -- anything is better than total darkness, when your eyes will routinely lose some of their adaptation from the bright image cast by the enlarger, and all that's really needed is some way to confirm the emulsion side of the paper without leaving fingerprints, and to be sure the paper is correctly aligned in the easel and submerged in the chemical trays.
But I distinctly recall being told by a friend who had done RA-4 printing that the darkroom wasn't all that dark.
Which is it?