A sticky diaphragm usually means that the grease from the helical has
broken down into a thick oil. It flows along inside the lens until it
gets to the diaphragm blades. The thick oil causes the blades to be
sticky. Then can be just sluggish or frozen open or closed.
Since the blades are snappy when using the camera's activation lever
(the inner tab) the blades do not have oil on them which is very good
news. Using the DOF tab, however, does nothing other then press on the
same aperture lever used by the camera but inside the lens rather than
outside. If you watch the inner tab while you press the DOF tab you
will see that both move together.
Since only the DOF tab operates sluggishly it means that the problem is
only in that linkage. The DOF tab presses on a semi-circular ring that
is about half the circumference of the lens. It pivots on a single
screw not far from where the DOF tab contacts the ring. Sluggish
operation would seem to mean a loose screw, dirt or maybe even oil on
the ring. In other words it likely needs a screw tightened or simple
cleaning. Fortunately, it's very easy to access. I copied some repair
text from an old message from Don Gaiken...
-----------------------------------------------------------------------
...remove the three silver screws from the mount. The rear mount will
just slide off. There are two tabs sticking out of the inside of the
mount. One goes into a fork attached to the aperture's cam ring. The
other actuates the aperture - it's spring loaded. To reassemble, just
align the free tab (the one that's not spring loaded) so it will go
between the legs of the fork, then turn the mount so the screw holes
line up. Turning the aperture ring on the front should move the tab
sticking out of the back of the lens both ways. If it only goes one
way, try again - you've missed the fork. And when you move the aperture
lever on the back of the lens, the diaphragm should close - if not, try
again - you're on the wrong side of the lever!
------------------------------------------------------------------------
Chuck Norcutt
On 7/17/2013 1:33 PM, Vick Ko wrote:
> By the way, my iris is "snappy" if I use the inner tab (the one the
> camera body activates) but sticky if I use the user DOF tab.
>
> Is that the characteristic failure mode?
>
> Vick
>
>
>
> hOn 17/07/2013 1:23 PM, Vick Ko wrote:
>> My 50/1.8:
>>
>> - “Japan" on the front ring
>> - full lettering is " OLYMPUS OM-SYSTEM ZUIKO MC AUTO-S 1:1.8 f=50mm
>> Japan " , caps and lower case as presented
>> - all black front
>> - sn 2756466 on the rear-most silver ring that has the DOF scale
>>
>> So which version do I have? I'm thinking Type 3.
>>
>>
>> regards
>> Vick
>
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