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[OM] Lens/Body interface question

Subject: [OM] Lens/Body interface question
From: "Curtis P. Hedman" <Curtis.P.Hedman-1@xxxxxxxxxx>
Date: Sun, 13 May 2001 21:38:45 -0500
I have a question about the tolerance spec on the length or depth of the aperture coupling pin that sticks out of the back of OM-mount lenses. This is the pin that picks up the spring loaded tab at the left edge of the inside of the body mount and couples in the lens aperture setting, I believe. I have a lens (a Vivitar 80-200 f/4 zoom) that gives me problems occasionally in that proper metering sometimes does not occur, usually after I've carried the camera around with the lens mounted. After some patient fiddling, I noticed that once in awhile, by moving the aperture setting ring back and forth, I could induce the failure which was proceeded by a sound like a spring-loaded part snapping to its stop. Sometimes this sound occurred as the lens was being seated, in which case it again failed to meter properly. Under inspection, I decided the sound I heard was that of the body mounted spring loaded indexing tab slipping pat the aperture pin on the back of the lens. Being ever more curious, I used a crude gauge to measure the depth of the body tab below the face of the mount (6.0 mm), and then measured the protrusion of the coupling pin relative to the lens mounting surface for four OM-mount lenses I have access to - a Zuiko 50mm f/1.4, a Zuiko 50mm f/3.5 Macro, a Tokina 35-105mm f/3.5-4.8 zoom (now a collection of random parts, except for the mount/pin), and the Vivitar Zoom in question. The two Zuikos and the Tokina all came in at 7.0 to 7.1 mm, while the Vivitar measured out to about 6.2 mm... which, given the limited precision of my measurements, does not seem to be long enough for reliable positive engagement.

Anyway, all this is speculation and deduction based on a few simple measurements..... Does anyone have actual spec data on how long the lens aperture index pin is supposed to be? And, for that matter, does it seems at all possible that the length can be adjusted (extended) without major surgery to the lens? Given the added mm in length of the Zuiko lenses, I have no reason to believe that it is the body (an OM-4T) that is out of spec -- but again, this could be a hopefully deduction on my part!

I'm new to the list, so I hope this sort of question is appropriate and acceptable. I eagerly await your thoughts and information.

Curt Hedman


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