FotoDave@aol.com
Fri, 05 Mar 1999 11:07:09 -0500 (EST)
In a message dated 3/5/99 7:31:15 AM Pacific Standard Time,
tomf2468@pipeline.com writes:
> But with very careful development and VERY
> careful exposure it has a nice (if short) linear area. I've found (I'm new
> using this, so take my comments with "salt") that a near perfect exposure
> is needed to insure you don't loose highlight of shadw contrast.
Exactly! That is because the "exposure range" (the range where we have nice
separation) of lith film is short, so one must place the exposure so that
every details fall within this range.
I am planning to write on "exposure range vs. density range." This will
hopefully clear up all confusion or mystery concerning lith film. I will
probably post it on my web site. That way I can explain clearer with charts
and diagrams.
For now, I just want to say that when we use dilution to change contrast, we
are mainly changing the Dmax. We can't change the exposure range because that
is the characteristic of the emulsion. Please look at the lith article in PF
issue #2, Fig. 1, 3, 4. You will notice that with dilution of Dektol and with
D76, we were able to reduce Dmax from 3.3 to 2.1 to 1.35 (I am using the
graphs from the 3.5 min development). This is a significant improvement in
lowering Dmax! However, note that the number of steps where you can have
linear separation remains the SAME in all cases!
Therefore a carefully formulated formula for using lith film does/should not
simply lower Dmax. It has to lower the contrast to a particular range so that
it is compatable to the shoulder, thus the shoulder region becomes usable
region. In that sense, while the exposure range cannot be truly extended, it
acts like it is extended (this part will be briefly explained a little in my
next article).
Sorry for posting this reply to this reversal thread, but the characteristic
of lith film is the same for normal or reversed processing (except that for
reversal processing, there is an extra requirement of getting high Dmax in the
first development in order to get low Dmin for the reversed negative. This has
been explained by Liam both in his article and online, so I won't repeat).
Dave S
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