In a message dated 11/24/04 7:08:11 AM, astrobound@yahoo.com writes:
I'm sure this is an old can of worms but... Where are
the best links for "personal best techniques" for
hypering Techpan in 120? I have a Lumicon 600 setup
with both temp probes and a high vacuum pump. I've
heard that the later emulsion can be hypered in the
paper backing without the Kodak Nebula problem. If
possible I would like to remove the backing after
hypering for use with a vacuum back camera. My main
interest is with the use of the high vacuum pump and
how many cycles are needed to dry the film before
hypering? I've also heard Nitrogen instead of forming
gas can be used for the prehyper vacuum treatment?
Keith
Keith:
Can of worms is right.
Jason Ware's previous post is correct.
Tech Pan 120 has and has had a ink imprinting problem since about 1999.
Because the paper backing is printed and rolled up so that the ink touches the film emulsion,
the 'type' becomes visible on the film when vacuum dessicated, hypered and developed.
You can actually read Kodak and the frame numbers on the film. It is faint, but legible enough to
mess up an image. Supposedly Kodak changed the inks from solvent based to water based, causing the problem to appear in about 1999. (water/moisture is the enemy of hypered film) About 2001 or so, Kodak said they changed the backing material from paper to a plastic and the problem seemed to go away, however as of a couple of years ago it was still evident.
I too, changed to 4x5 Tech Pan which I cut down and hyper for my Schmidt camera.
Using a high vacuum pump to dessicate the film seems to make the imprint problem worse, so one might conclude that using the old 'hand pump and flush' method might work, but the hypering would not be as complete.
For a developed fog level, over base fog level of 0.4 or 0.5 I dessicate 35mm and 4x5 Tech Pan for 8 hours at room temperature, with the vacuum pump running, to 30-40 microns. I add Forming Gas to 15 psi at room temperature. I heat the tank for 8 hours at 50 degrees C. I then turn off the heat and evacuate the tank with the pump, let the tank cool and remove the film. The film is processed in D-19 at 68 degrees F for 7 minutes. This combination produces the 0.4 to 0.5 density I use with the Schmidt camera, which is f1.5. Some, with slower optical systems, like f6-f9, prefer to process up to 11 minutes.
Kent Kirkley
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