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[OM] Infrared & dimpled pressure plates

Subject: [OM] Infrared & dimpled pressure plates
From: Josh Putnam <josh@xxxxxxxxx>
Date: Wed, 19 Dec 2001 09:27:39 -0800
>Lately, I've been tempted to try my hand at infared photography.
>I've been doing a bit of web based research on tips and
>techniques and I discovered that the dimpled pattern on the
>film pressure plate on OM backs may cause a problem with IR
>film. Has anyone here witnessed this?

I have seen this with my OM-1 and Olympus 35-S rangefinder.  It's
a problem specific to Kodak High Speed Infrared -- HIE has no
anti-halation layer, so that incoming light goes through the film
and reflects back into the film off the pressure plate.  The
dimples act like tiny little concave mirrors and concentrate
their reflected light, making a pattern of higher-density dots on
the negative.

The problem gets more visible the deeper your filtration gets,
e.g. you'll barely notice it with a 25 red, but it will be quite
pronounced with an 87C.  It also gets more visible if you shoot
the film slow, for a lower-contrast, higher-halation image.

I have one OM-1 body dedicated to IR use.  Besides having an
internally-mounted 87 gel filter, it has black backing paper from
120 film taped over the pressure plate, eliminating the dimple
effect.  (If not otherwise noted in the descriptions, just about
every picture in my IR gallery was taken with this setup, see
http://www.phred.org/~josh/photo/ir.html)

-- 
          josh@xxxxxxxxx is Joshua Putnam
            http://www.phred.org/~josh/
     Updated Infrared Photography Books List:
   http://www.phred.org/~josh/photo/irbooks.html

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