Hey, here's a real, live, nitty-gritty, on-topic OM post!
I have a 28mm 2.8 which will not open (using the diaphragm ring) to more
than f/5.6. The diaphragm blades open fully when the DOF preview button
is not depressed but the diaphragm ring can't be rotated to either f/4
or f/2.8. It hits a hard stop at f/5.6.
I assumed that there must be a problem with the detent ball but was
surprised when I removed the filter/detent ring and found that the
detent mechanism is fine and there is no appreciable wear on the ring.
I tried rotating the diaphragm ring again without the detent ring and
ball installed and it still hits a hard stop at f/5.6. Then I tried to
lift off the diaphragm ring and was surprised to discover that I
couldn't. I can lift the side opposite what I'll call the diaphragm
coupling pin (CE157300 on the parts diagram) but that pin acts like it
has a hook on the end. The pin side lifts no more than 1/2mm and stops
cold just as though what I think should be a flat bladed pin has a hook
on the end and is catching on something.
Any suggestions? If I remove the lens mount will I be able to see the
inside of the barrel and figure out what the obstruction is? I guess I
could also remove the two screws attaching the diaphragm ring to the
coupling pin but I hate to disassemble what I don't have to.
Thanks,
Chuck Norcutt
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