[pure-silver] Re: Modified Agfa 108 with multigrade paper
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Thu, 15 Mar 2007 19:04:45 -0700
----- Original Message -----
From: "hksvk" <hksvk@xxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, March 15, 2007 4:37 PM
Subject: [pure-silver] Re: Modified Agfa 108 with multigrade
paper
Thank you for your helpful responses, especially the one
correcting my
notion that I should be able to increase contrast to the
extent I want by
using a high contrast developer with the same paper.
I am using the El-Nikkor 105f5.6 enlarging lens. Isn't
this a pretty good
one? It shouldn't be a cause for uneven or irregular
densities, should it?
When intensifying a negative with Kodak Rapid Selenium
Toner, is it
necessary to first treat it to 'harden' it, ie., to
prevent blotching or
other unevenness? with formaldehyde?
Harry
I don't have direct experience with the El-Nikkor but
its supposed to be one of the three best on the market.
105mm is slightly long for 2-1/4 x 2-1/4 ("normal" is 75mm
or 80mm) so its fall off should be a bit less. All
"standard" lenses have fall off which approximates cos^4
theta where theta is the image half-angle. There are lenses
with more and some with less. In any case, I don't think the
lens is the problem.
For best illumination with a condenser lamp house the
condenser should be focused at the entrance pupil of the
lens (for enlarging the entrance pupil is on the side facing
the negative). This is approximately somewher between the
rear surface and the iris. Its not _that_ critical. It may
help to get an approximate focus by first focusing the lens
with a negative in the holder for the size image you want.
Then remove the lens and the negative and hold a piece of
paper under the lamphouse, you should have an image of the
lamp itself focused somewhere around the back to the middle
of the lens. Once you have this replace the lens, replace
the negative to make sure its still in focus. Then remove it
and fine focus the condenser for the best uniformity of
illumination. In theory this should be done with the lens
wide open but I would check it stopped down a couple of
stops too. Use an enlaring meter to check the illumination.
You may still have problems if the printing contrast is high
enough. If the uneveness is just fall off from the center
you may be able to correct it by using a round card to burn
in the corners. I card cut from black print mount cardboard
works well. Tape it to some wire, an unbent coathanger works
well, as a handle. You will need to experiment to get it
right but the enlarging exposure meter should give some
guidance.
Kodak Rapid Selenium Toner has the virtue of not
damaging the emulsion, no special hardening is needed. I
suggest pre-soaking dry negatives for a few minutes before
toning to insure even take up of the toner. 1:3 dilution
probably will work too fast, begin with 1:9 and if it isn't
going fast enough put more toner in (after taking the film
out of course). The negatives can be washed, dried, and
tested and then toned more if needed. At some point the
toner will have toned as far as it can. The amount of
intensification available from KRST is limited compared to
some other intensifiers but it is safe for the film and for
you and is easily available. KRST was used for many years as
an after treatment to protect images against oxidation and
sufiding. It was discovered that the very slight toning
given for this purpose was not always effective so other
methods were gone to. However, enough toning to intensify
the image detectably is enough to give it full protection so
the intensified negatives will be very long lived.
I would experiment on a single negative, perhaps one of
minimal importance. Follow toning with about a 30 minute
wash. Less may be sufficient for film.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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