The rear lens stop down ring does push on a lever inside the lens. This
lever with a long slot (ZD3030) has a pin riding in it (arm of ZJ1031).
That pin slides to a spot determined by position of f stop cam, then
spring (CB0868) is free to pull diaphragm plate to stop blades down.
Levers only force other levers to a certain point in the block
diaphragm, then parts rely on springs to pull them closed. I've never
seen a lens of this design that had so much oil that diaphragm did not
close but I think it could happen. 50 1.8s are very different but still
rely on tiny spring to reopen blades which often cannot overcome oil
buildup
___________________________________
John Hermanson | CPS, Inc.
21 South Ln., Huntington NY 11743
631-424-2121 | www.zuiko.com
Olympus OM Service since 1977
Gallery: www.zuiko.com/album/index.html
Chuck Norcutt wrote:
> If there was a direct mechanical connection on closing of the blades
> then a lens whose blades were completely stuck open (John's "extreme
> case") would cause the camera to jam and the aperture activation arm in
> the camera would be blocked from operating. It could not rise up and
> move the diaphragm lever in the lens, the mirror couldn't rise and the
> shutter couldn't fire.
>
> Chuck Norcutt
>
>
> Carlos J. Santisteban wrote:
>> Hi John, Chuck and all,
>>
>> From: John Hermanson
>>
>>
>>
>>> I've seen Cosina lens quality and FWIR (from what I recall) it's not even
>>> close to 35-105 quality. I have always thought Tokina.
>>
>> Most likely. Cosina branded lenses were usually aimed to the
>> amateur/entry-level.
>>
>> However, Cosina has made bodies and lenses for many brands, with huge range
>> of quality. For instance, I've seen inside a Cosina-made Y*shica FX-3 (which
>> is a rather reliable little beast) and a 'Centon' camera -- essentialy an
>> FX-3 in K-mount. But build quality had nothing to do with the Y*shica,
>> despite both coming from the same maker.
>>
>> Cosina is currently making some fine rangefinder lenses under the
>> Voigtländer brand, although some of the older Bessa bodies had a toy-like
>> build quality :-(
>>
>> BTW... I have ordered from S. Gandy an Ultron 28/1.9 in LTM. Next purchase
>> (as money permits!) will be the 21/4... and the 40/1.4 in Leica-M mount
>> should follow ;-)
>>
>>> Oily diaphragm may eventually spray a fine coating of oil all over the 2
>>> elements that face it.
>> That is a real risk, although probably only in extreme cases. Another risk
>> may be internal flare caused by the reflection on the shiny oil instead of
>> the dark matte blades...
>>
>>> From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>I think Carlos is wrong
>> here.
>>
>> I may be wrong, of course. I haven't taken apart any Zuiko (safe for
>> removing a dead bug from a silvernosed 50/1.8!!!) and internal layout of
>> mechanics may vary depending on the particular model.
>>
>>> He implies there is a direct mechanical
>>> connection to the blades
>> However, I have repaired several OT lenses with oily diaphragms and direct
>> connection to the blades was definitely the case there, so I assumed Zuikos
>> would be the same.
>>
>>> when closing down such that oil can't cause
>>> problems on closing but there is only a weak spring on return which can
>>> lead to sluggishness with oily blades.
>> Again, most OT lenses are "normaly closed", so the weak spring is the
>> responsible for that, and may suffer from oily blades. But Pen-F lenses are,
>> like OM, "normally open" and I have seen at least one of these which didn't
>> close in a timely manner... it may depend on internal construction, really.
>>
>>> As your comment below makes
>>> clear ("shutter fires but does so without the blades stopping down")
>>> that can't be the case.
>> I think the key here is what followed that John's quote:
>>
>>> (that's an extreme case)
>> Of course, I can only speak from my experience, but have checked again the
>> 50/1.2 @ OM2 (which doesn't show oil in the blades that I can see, but has a
>> rather stiff auto-diaphragm pin -- maybe is a completely unrelated fault?)
>> and, when "releasing the shutter" (i.e. pushing the button) it takes about
>> half a second for the blades to close, and *then* (already at the proper
>> shooting aperture) the shutter actually trips (checked also by looking from
>> the back of the camera, open without film).
>>
>> So I'd like to raise a question... how many of us had overexposure problems
>> _actually_ related to a sluggish diaphragm, and with which lenses? Please
>> note that my "theory" won't apply to the OM-2S, PC and 40, because of the
>> different diaphragm action. Another possible, unrelated problem is in
>> _manual_ or spot mode, when an oily iris won't open completely after
>> exposure (that's the behaviour of my 300/4.5, BTW) throwing off meter
>> readings somewhat. Won't affect OTF, though.
>>
>> It's really nice to learn so many things on this list...
>>
>> Cheers,
--
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