FotoDave@aol.com
Mon, 08 Mar 1999 15:19:44 -0500 (EST)
> Could you explain it better?You first determine the maximum flash the film
> can take before reaching 0,10 density in the positive, than test trip to
> determine exposure with that flash, is that it?
Hi Joao,
I would suggestion the following:
1. Use dilution and development time of the first developer to determine the
overall contrast. The required density range depends on what you consider
"normal" negatives and the process you are using. I prefer development time of
about 6 mins because shorter than 5 mins might cause unevenness whereas more
than 7 mins is inconvenient especially if someone is using tray processing.
2. Determine maximum flash. Yes, as you described, this would be the amount of
flash so that the "positive" will have a density of *approximately* 0.10 + b +
f. The 1.0 does not have to be that precise, but the figure is good for Arista
APH film. With this maximum flash, you get the best separation that you can
get. So the next thing is the determine exposure to get good highlight and
shadow separation.
> If it is, you than determine the dmax by choosing an appropriate X factor?
3. Yes, except that I don't use a multiplication factor (actually I could
since I have a densitometer, but I think what I will describe here will be
easier for those w/o densitometer and also, somehow we ultimately need a
visual check).
What I do is I estimate the correct exposure for positive (this can be done by
a test strip, densitometric reading, or probe reading of an exposure meter
like EM-10), then I arrange my 4-blade easel so that I can expose the same
area six times on a piece of film. The area chosen would have darkest,
lightest, shadow separation, and highlight separation. Then I would expose
with 2x, 3x, 4x, 5x, 6x, 7x on one sheet and complete the reversal processing.
>From this, you should be able to determine (even visually) which one has the
best separation.
This simply means you shift the exposure / scale up and down but since the
exposure range of lith film is short and is NOT linear, you shift it up and
down to see which exposure give you the best / desired separation.
Of course, if your original negative has short range, then you don't even need
to flash since you will be able to find one exposure that give your both good
highlight and shadow separation, otherwise use the flash.
If all 6 exposures are under or all over exposure, you have mis-estimate the
base exposure, so re-do (unless you feel that you can make judgement based on
the strips). If some looks under and some over exposed, you should be able to
choose which exposure is best. If no matter how you shift, you either lose
highlights or shadows, then the original range of your negative is too high
for the lith film. You need to use other methods (e.g. Liam's suggestion on
filtration and my suggestion on LC-1 + reducer....) or use a continous-tone
film.
Note that what I said above applies to both normal or reversal processing. Of
course, although I didn't realize it, Joao has read that it also applies in
chess playing.... :)
Beside the suggestion of low-contrast developer + reducer, I actually had
another suggestion that at some point I thought would not work, but now I
think it might, so I am simply laying this out to all again. Maybe someone
with convenient setup can do a quick test. The idea is to use a low-contrast
second developer. However, one must have a clear understanding that the low-
contrast developer is not any one that is simply lowering the Dmax. It must
lower it to a point that the scale appears to be lenghtened. One can start
with LC-1 2:2:6, for example or any very low contrast developer that one is
familiar with. There is nothing unusual about LC-1, so I don't want to sound
like I am over-recommending it. It is just simply that I have tested that at
particular dilution and particular development time, the contrast is low
enough to make the overall curve look like a straight line.
Of course, when one does this (underdevelopment of the re-exposed film), the
final fixing is no longer optional but is required.
Dave S
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