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Re: [OM] Oily 300/4.5. Suggestions?

Subject: Re: [OM] Oily 300/4.5. Suggestions?
From: "Carlos J. Santisteban" <zuiko21@xxxxxxxxx>
Date: Thu, 4 Jun 2009 10:40:33 +0200
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,
-- 
Carlos J. Santisteban Salinas
IES Turaniana (Roquetas de Mar, Almeria)
<http://cjss.sytes.net/>
-- 
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