From: Richard Knoppow (dickburk@ix.netcom.com)
Date: 12/28/01-04:12:14 PM Z
At 06:39 PM 12/17/2001 -0600, you wrote:
>Hi:
>
>This just a little off topic, but not too far...
>
>Was reading an old reference on photochemistry and came across a very
>small section on latentsification (SP?!). This is the practice of
>treating film after exposure, but prior to development to increase a film
>sensitivity.
>
>Most of the techniques are bizarre and impractical but a couple looked
>practical. One was soaking the film in a solution of oxalic acid before
>development. I tried this and it did alter the way the film developed it
>did not appear to increase sensitivity - the film wasn't denser.
>
>Does anyone have any experience or even success, with anything like this?
>
>Gord
>
>
>
>---------------------------------------------------------
>Gordon J. Holtslander Dept. of Biology
>holtsg@duke.usask.ca 112 Science Place
>http://duke.usask.ca/~holtsg University of Saskatchewan
>Tel (306) 966-4433 Saskatoon, Saskatchewan
>Fax (306) 966-4461 Canada S7N 5E2
>---------------------------------------------------------
>
You will find a good deal on latensifying and the related
hypersensitising in books or web sites about astrophotography. An example
is: _A Manual of Advanced Celestial Photography_, Brad D. Wallis and Robert
W. Provin, 1988, Cambridge University Press ISBN 0 521 25553 8
Hypersensitizing is used quite extensively. Its main effect is to
substantially reduce reciprocity effect, which is very important in
astronomical photography where very long exposures are the rule.
Flashing film can also be used to increase effective speed by lowering
the contrast gotten with a given development time.
So called pushing of film really does not increase its speed. It
increases contast. The low densities are brought up a little, which gives
an effective increase in speed, but at the expense of very high contrast.
---- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com
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