> Still, I'm surprised to find "circles of confusion" (which I once
> understood *perfectly*) applied to contact printing. Aren't the optics
> different?
Hi Judy, I'm no physicist and am probably misusing the term circle of
confusion, but since we're dealing with points and the fuzzy edges of
circular patches of light maybe it's not stretching the "circle of least
confusion" too far.
Tests are the only way to go. I'm not clear how the aluminum foil wrapped
around the base of the fluorescent fixtures should have been destroying
definition or why anybody would want to do this anyway.
> I'll try to rig up vacuum frame with the fluorescents for a test, but
> meanwhile another finding suggests I may abandon them for gum. I haven't a
> clue why, but the limited tests I've done so far show that the pigment is
> richer and shadow steps deeper with the NuArc. Does anyone have a theory
> for that?????? (I have found no difference with cyanotype.)
How about the theory of reciprocity effects? Perhaps there's a
considerable difference in light output between the two sources causing a
change in contrast, assuming an identical exposure time. Even if you
increase the time to compensate for the fluorescents being a less intense
source, it may not necessarily follow that you'll achieve the same
exposure, because what's supposed to be the reciprocal relation between
light level and time breaks down, with unusually long printing times
resulting in a loss in speed and image contrast. I have found differences
with cyanotype - the sun gives quite different contrast to UV fluoro
tubes, so your results are curious. Maybe the effect is much more
noticable with the much shorter exposures for gum?
Regarding diffusion "in the paper itself" or swelling fibres (or fibers)
you're absolutely right. I was trying to suggest the unsharpness wasn't
due to the light source at all, but might be occuring because of other
factors.
> Be careful outdoors, Philip......a lot of cosmic rays going around.
> With the windchill factor it's 19 degrees fahrenheit here tonight. Sure
> glad I don't have to risk dangerous radiation from sunny skies.....
Everybody here is getting paranoid about skin cancer, which is introducing
new problems. Yesterday I got some SP15 blockout in my eye, which
represents a completely new type of danger!
Philip