The pin on the 28 2.8 is L shaped and connects to the diaphragm control
cam through a slot in the main tube. To remove the ring, you'll have to
take out the 2 screws holding the pin in. Unscrewing the front lens
assembly, which would expose the diaphragm mechanism, should reveal what
the problem is.
___________________________________
John Hermanson
Camtech Photo Services, Inc.
21 South Lane, Huntington NY 11743
631-424-2121 | Olympus OM Service since 1977
http://www.zuiko.com | omtech1 AT verizon.net
Chuck Norcutt wrote:
> 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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