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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