Nick Makris (nick@mcn.org)
Sat, 06 Mar 1999 13:48:53 -0800
Liam and all,
This seems somewhat similar to a process I use to make B&W prints from color
negs using standard B&W paper - the key here is that it's not Panalure or
equiv. In my experience with this method of making prints, I found there is
a subtle shift of relative colors particularly in the human face (it does
get darker with certain packs). In any case, by dialing in the equivalent
of a Polycontrast filter and an offsetting pack for the color base of the
particular film emulsion, you are definitely able to control contrast. The
color sensitivity of the receptors in the two situations are somewhat
different, however, it seems analogous.
Nick Makris
-----Original Message-----
From: Liam Lawless <lawless@vignette.freeserve.co.uk>
To: Alt Photo <alt-photo-process-l@usask.ca>
Date: Saturday, March 06, 1999 12:55 PM
Subject: Help Wanted
>Hi everyone,
>
>This concerns an idea that popped into my head when I couldn't sleep last
>night (actually, 6.55 AM this morning) - it sounds crazy, I know, but I
>can't see why it shouldn't work. How well I don't know, but I'm not able
>to test it myself as I don't have a colour enlarger or colour printing
>filters, so what I'm hoping for is someone to tell me where my logic is
>wrong, or for someone who is convinced by it to give it a try and see if it
>works.
>
>Going back to Joao's original query about contrast control for lith
>reversal, what I think is needed, were such a thing possible, is a short
>base exposure for the shadows and a long base exposure for the highlights.
>I believe it may be possible to do something similar with colour filters.
>
> WHEN YOU'VE ALL STOPPED LAUGHING, I'LL CONTINUE....
>
>I'll explain carefully, and apologise for the fact that this means talking
>down to most of you. Now, a lith emulsion, as I understand these things,
is
>not colour-sensitised, which means that its sensitivity lies predominantly
>in the blue-violet (and UV) spectral region. Correct so far? If so, then
>light of different colours will have different actinic power as far as lith
>is concerned, depending how much or how little blue its colour contains: a
>blue light affects the film more than a green one (blue+yellow), and a
green
>more than orange (yellow+red), and so on.
>
>The important thing is that I would expect a blue light to affect lith more
>than a magenta light (blue+red) of the same intensity. Now, suppose we
>project an original camera neg onto lith from a colour enlarger head with
>maximum magenta filtration dialled in, and a pale cyan filter (say about
>25C) held under the enlarger lens. Lots of magenta light will pass through
>the shadows of the negative and its colour will be relatively unaffected by
>the pale cyan filter that it must also pass through, but in the highlights
>where only a little magenta light can pass, the effect of the filter under
>the lens is much greater, and magenta+cyan, according to the rules of
colour
>printing, equals blue, which has more actinic power on lith. The same
>filter factor applies to both shadows and highlights, so what I believe we
>have done with our filters is to hold back the shadows and augment the
>highlight exposure at the same time.
>
>Well, am I mad??
>
>
>
>Liam
>
>
This archive was generated by hypermail 2.0b3 on Sat Nov 06 1999 - 10:06:55