Thanks for the help. The problem is fixed. The lens must have been
repaired and mis-assembled some time before I got it and apparently I've
never tried to use it until recently or, if I did, never attempted to
set it wider than f/5.6.
The problem was that the diaphragm stop down lever driven by the camera
(CE1049) which is supposed to fit into the wider of two notches in
CE1584 was on the outside of the notch and not inside the notch. The
aperture control pin (CE1573) also fits into a notch in CE1584 but into
the smaller of the two side-by-side notches. It was properly in the
small notch but, since the stop down lever was outside of its own notch
in CE1584, when the aperture control pin would cause CE1584 to rotate
CE1584 would run into and jam against the misplaced stop down lever
before completing its full travel.
It took removing the front lens assembly as you suggested to see what
the problem was but the fix had to be implemented from the back by
removing the mount so the stop down lever could be lifted and inserted
into the notch in CE1584.
Add "mis-assembled 28/2.8" to your list of symptoms and fix file.
I think this may be the first time I've ever "easily" removed a thread
locked lens assembly with a little bit of acetone.
Thanks again for the help.
Chuck Norcutt
John Hermanson wrote:
> 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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