Dear Leigh,

Sorry for the confusing phraseology. What I meant by that was that my own visual system was not focusing substantially differently using different colors of light. There are two possible sources of focus error. One is the shift in real focus distance as a function of wavelength. The other is the Gainer effect and related ones-- the human eye not focusing different wavelengths the same way. What I was saying was that for me this latter effect measures as small in size compared to the former.

Anyway, I didn't focus using magenta light, so it doesn't matter.

Please reread pages 148-150 and study the graphs in figures 11-9 to 11-11 until you really understand them.

It is not relevant that the short wavelength component (NOT just UV, deep violet counts, too-- I consistently talk about "UV-violet" light in the book) is a small amount of the total radiation. What is relevant is the convolved result of the lamp emission spectrum, the enlarger lens transmission and the paper spectral response. In and of itself, the Zeiss curve is meaningless.

pax / Ctein
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