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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