Re: copy negatives

eml@gate.net
Thu, 14 Sep 1995 09:02:22 -0400 (EDT)

Paul Simon
>
> I've been away for about a week and a half on vacation, but I
> see that before and after that time, there have been a number of
> notes about making enlarged copy negatives. It's of great
> interest to me, as I have several decades of 35 mm black and
> white that I want to go through and make a few pt prints. The
> problem I have with all the discussions is that no one seems to
> be addressing the issue of fidelity of transfer. I have been
> looking at Agfa N31P as sold by Palladio, and using a
> densitometer, find that it is quite linear at gamma =1 above a
> density of about 0.5. I have not yet checked at higher gamma but
> suspect similar results. The instructions in the Palladio manual
> for using this stuff are pretty good but semi-quantitative. It
> would seem that to get a useful, linear transfer with this
> material would cause one to suffer about a 4 times exposure
> penalty therefore, by being forced to stay about .6 above B+F.
>
> Does anyone have densitometric data on other copy processes? Is
> it important/significant enough to worry about? Comments?
>
> Paul Simon
>
I have been wondering about the same thing exactly, as the lack
of large negatives has prevented me from working in any
alternative processes at larger than 6x6 negatives for test
contact prints.

Looking in the Kodak data book for black & white films, I
have noticeds the extremely straight exposure/density curves
for the *556 series Ortho Litho films. There is hardly any
'toe' at all, and control of gamma is no problem, as I
found out by processing a 4x5 sheet in dilute Microphen.

I have been thinking that processing in a two-part developer
similar to one that I brewed up for Tech Pan might produce
an extended exposure range, if needed. The problem as I
see it is to eliminate the 'toe' effect, as you have said.
One way that just might work would be to post-process the
fixed negative in a dilute 'cutting' reducer, whose effect
would be progressively more severe on the thinnest densities.

For sheer cheapness, though, a Litho working negative would
be ideal, if the correct combination of exposure and processing
can be achieved. It should be no more necessary to worry
about 'toe' on the enlarged printing negative than on the original
one. In fact, if an interpositive is generated, the toe is flipped
anyway, so print it as darkly as you like, avoiding the toe,
then perform a cutting reduction on the lowest values of the
enlarged negative and you should have a straight line!

A further thought. Perhaps in the developer used on the enlarged
negative, it might be possible to include a small amount of
Potassium Thiocyanate, as is done in reversal first developers.
This would effectively reduce the thinner areas as development
proceeded normally elsewhere on the film.

Just a few ramblings. Hope they give you an idea or two.

Ed Lukacs

-- 


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