Re: Great Enl. Negs - Better
Luis Nadeau (nadeaul@nbnet.nb.ca)
Thu, 29 Jan 1998 10:44:19 -0400
At 2:05 AM -0400 98/01/29, Sandy King wrote:
...
>Richard Knoppow writes: "Unless alternative printing materials have much
>different spectral characteristic then I think they do (sensitive to blue
>and near UV, with no effect on contrast caused by the color of the exposing
>light) a Pyro negative should print no differently than a somewhat higher
>contrast negative made with a non-staining developer."
>
>This statement is clearly at odds with my experience with carbon printing.
>To the contrary, as Kerik comments with respect to platinum/palladium
>printing, what I observe is that the range of highlights is greatly
>extended. Perhaps the theory of Richard's reasoning is flawed because it
>does not take into account the fact that the sensitivity of some of the
>alternative process emulsions extends into the green portion of the
>spectrum. From testing I did a couple of years ago I found that dichromated
>gelatin has considerable sensitivity to light at 500-600 na, and even
>beyond.
The yellow color from your neg, the yellow dichromate itself and/or your
pigments affects contrast characteristics significantly. Yellow colors tend
to give much less contrast and less speed. The type of light source has a
strong effect. All other factors being equal, the length of the exposure
affects contrast significantly. My books have discussions on these
variables.
Luis Nadeau
NADEAUL@NBNET.NB.CA
Fredericton, New Brunswick, Canada
http://www3.nbnet.nb.ca/nadeaul/