U of S | Mailing List Archive | alt-photo-process-l | Re: STARTING POINT


From: Don Bryant <dsbryant@bellsouth.net>
Date: Mon, 21 Apr 2008 22:35:49 -0400

> Some individuals that contact print large format negatives
> report that contact prints made on graded paper are sharper
> than contact prints made on RC paper. Again I've never seen
> the difference.

That's unlikely. The resolution of paper emulsion is pretty
low, much lower than camera film emulsions, and any difference
between graded and variable contrast papers is insignificant,
or wavelength-dependent at best.

In paper emulsions, silver halide crystals of 100 to 400
nanometers are most frequently used. These crystals have
pretty strong scattering of blue light and they give poor
resolution. On the other hand, film emulsions are usually
coarser than 400nm and they are also coated in at least two
layers, where coarser grain emulsion (less scattering) is
coated atop a finer grain layer. More heavily applied spectral
sensitization further improves absorption and hence scattering
of light.  Use of tabular grain is a further improvement in
reduction of light scattering.

Of course, the above consideration is irrelevant if you test
the resolution with x-ray exposure, which does not have this
sort of scattering problem.

I've not studied thse types of emulsions, but very fine grain
ones used for holography and IC pattern masks (about 20nm) are
much finer grained than the wavelengths of the light, and they
may not have the resolution problems.

Ryuji Suzuki
"The truth that I am seeking is in your missing file."
(Bob Dylan, Something's Burning Baby, 1985)