FotoDave@aol.com
Thu, 11 Mar 1999 17:02:37 -0500 (EST)
In a message dated 3/10/99 6:52:24 PM Pacific Standard Time,
lawless@vignette.freeserve.co.uk writes:
> The test
> subject was a Stouffer wedge, exposed for 3X the normal time and flashed 6
> seconds at the same aperture.
Hi Liam,
If you use a step tablet as the test subject, there is really no need to
specifically find the "normal" exposure than followed by 3x normal time. You
could expose it 3x, 5x or any time as long as you get the full scale in.
Exposure simply shift things up and down. That's why the x axis of a
characteristic curve of film is labelled *relative* log exposure.
Likewise, when I show my curve with different development, the main thing is
to show the complete curve. You will notice that step 1 to 7 in my curves are
in the shoulder (flat) region, but it doesn't mean that the film cannot
separate shadows. It simply means I exposed the film more to get the full
range. One only needs to find the full curve and then when true negative with
image is used, exposure so that it falls within the (separation) range you
want.
That's why I suggested to Joao the alternate method of determining exposure.
> Dave's idea a while ago was to make a much darker than usual neg by not
> overexposing, and take it back to the required density range in a reducer.
That was not really my suggestion. I would never thought that by exposing
without the 3x factor but processed the same thing would help anything at all
because that simply shift the scale, as described above.
> but I still don't see how it would help
> highlight separation that was not really there before reducing - this needs
> overexposure (the X-factor!) and doesn't happen without it.
Exactly. I didn't think and suggest that it would work. My suggestion was to
develop the first stage with a low-contrast developer (for example, yesterday
I used LC-1 to develop a negative (well, actually positive), than has 21 steps
of separation, both measurable and clearly visible). That was what I
suggested.
But I did mention also that with low-contrast development of the first stage,
one would get low Dmax and hence high Dmin after reversal, thus I wasn't sure
whether reduction could be used to cut down that much amount of fog.
But that was just my suggestion for anyone who might be interested in it. I am
currently using the positive/negative method and am quite happy with it.
> Low-Contrast Developer
> My tests so far with low-contrast developer have used Sil Horwitz's D-512
PP
> (phenidone-pyro) developer. Dave's LC-1 might have been a more useful one
> to start with, but I was attracted by the combination of phenidone and
pyro.
It depends on whether Sil's formula is low contrast for normal camera negative
or specifically formulated to lower the contrast of lith film. If it is for
normal camera negative, then I am sure it is still to contrasty for lith film.
For example, anyone using normal camera film could probably imagine how low
contrast they will get if they develop their film in D76 1+3 for 5 minutes,
yet you can see from my curve in PF #2 that D76 1+3 for 3.5 mins is still
contrasty for APH film! It lowers the Dmax significantly, but it didn't lower
the contrast so much that the shoulder region becomes usable region.
I now feel that it is so difficult to describe this kind of things with words
when there are charts and graphs in my mind; so I will give up for now. :)
Dave S
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