>What I've noticed is that when I turn off the blue lamp and make the negs
>using only the yellow, the grain is far less than if I were to use both or
>just the blue alone. I understand how this would work with variable
>contrast papers, but I'm confused by it working with a panchromatic film.
>The colours in the original slides are not predominantly blue or yellow
>either.
The effect lies not with the B&W film but in the original chrome. The
makers of chromes have had to use a faster emulsion for the yellow layer than
the cyan or magenta layers so that color balance will remain true. Faster
emulsions have bigger grain. When you use blue light you are "seeing" the
yellow layer and therefore you get larger grain. In color positives or prints
the eye has less ability to sharply image the yellow dye and therefore this
increased grain size is not objectionable.
When you use yellow light you "see" both the cyan and the magenta layers
which have smaller grain.
There are other effects which may be as important as grain size. If you
use a blue filter you will not have good separation of sky and clouds whereas
if you use a red filter the clouds will really pop out. These effects are the
same as when you use a filter on a camera when using B&W film. The use of a
yellow light will give a negative that is close to the luminosities that the
human eye assigns to colors and may be a good choice for the majority of
internegatives.
Greg