Charles Steinmetz (csteinmetz@redneck.efga.org)
Fri, 02 Apr 1999 15:00:49 +0000
Jewelia wrote:
>there are other differences between the sun, nuarcs, and lightbanks besides
>how they behave as point sources or not. it would be my guess that charles
>is right to say that he sees differences but i suspect that keith is right
>to say that there are no discernible differences between the printing of a
>point source and what i'll call for the moment a plane source instead of a
>light bank. what i suspect is more the cause of the differences some people
>see is the different 1) spectral ranges and 2) intensity or energy
>delivered at the print surface by the lamps. to really distinguish whether
>or not it was due to the "geometric arrangement" area of the lamp relative
>to the printing surface would not one have to conduct more controlled
>experiments say printing as per usual with a light bank for one print then
>moving that light bank far enough away such that it for all practical
>purposes is a point source while at the same time being able to crank up
>the energy such that the exposure time was nearly the same---which i doubt
>is exactly practical to do
There are certainly other differences besides the pointyness of the light,
and they affect some of the alt processes (in particular, by changing the
contrast). However, I'm convinced that the effect I see is unrelated to
these other differences and strongly correlated with pointyness. First,
the effect gets dramatically worse with even a thin mylar layer between
the negative and the sensitive material (the thinnest I tried was .0001"
-- one ten-thousandth inch, or one-tenth mil.). Second, the visual effect
is very similar to what one gets with less than perfect contact between
negative and paper -- sharp details get fuzzy edges, just like shadows
in the studio when you switch from a spot to a softbox. Finally, long,
long ago I did the reverse of your thought-experiment -- used opal glass
in a plate-burner -- and got results essentially identical to those with
the lightbank.
Best rgards,
Charles
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