Lens with OM mount - diaphragm problems?

[mhofmeist]

Hello,

I have got a little problem with a lens I aquired somewhat accidentally at a local bargain sale. It looks absolutely perfect, like new from the box, and the focusing ring moves smoothly. It had a Minolta rear cap so I thought I could use it with a Minolta SLR.
Now I see that the mount is quite different from Minolta SR. After some search in the Net it seems to be an Olympus OM mount. It has the two buttons at opposite sides which must be pressed to mount or unmount it. As far as I've read, this is specific for Olympus OM mount only.
It is a Tokina RMC 35-105 with close focus range.

The mount has two moving tabs or pins inside, probably connected with the diaphragm. When I stop down, one of these pins moves accordingly, so I assume that it would transfer the aperture to some mechanism in the camera body for exposure control. I have tried - very, very gently - to move this pin, but it does not budge. The other one, however, can be moved very easily, as I would expect.

The problem: On the Minolta lenses, which I am familiar with, I can by gently moving a similar pin open the stopped down diaphragm. It closes again when the pin is released. I routinely do this when checking a lens I consider buying, so I can see whether the diaphragm closes snappily as required.
In this lens it is different. The diaphragm does not close at all when I move the aperture ring.
Having no experience with Olympus OM mount lenses I have to ask, whether this is to be expected, or the diaphragm mechanism is damaged.

If the lens is ok, I would like to sell it. (I am out of work , every Euro is welcome).
If the diaphragm is just stuck or something, a repair should be worth trying, as it seems to be easily accessible for someone with a little experience in such work. In this case I would give the lens away for cost of shipping.
What I want to avoid is it to be thrown away. Tokina lenses are not so bad, and it is like new. Anyways - cameras, lenses and similarly sophisticated devices are not disposables.

Could someone who has experience with this lens mount be so kind and help to clear the matter up?

 

[Peltigera]

On an OM lens, when NOT attached, the movable pin should close the diaphragm when moved - the aperture ring will not directly alter the diaphragm when turned.

One of the two buttons on the bayonet mount should be a depth of field preview button, only one of them is used to demount the lens.
Sent from my A1-840 using Tapatalk

 

[Sean Mac]

The "pin" you can't move with your finger should move if you turn the aperture ring?

Looking at the lens with it pointing away from you and the red dot at "north" this pin is in the "north to east" quadrant.

With an OM lens the aperture does not close as you turn the aperture ring.

The lens release will be roughly NNW and the stop down at SSE.

I have an OM 85 in my hand as I'm writing....

Hope this helps. Good luck finding work too.

 

[thuggins]

There are two buttons on the mounting ring of the lens, but only one is the lock/release. The other is the DOF preview. Even with the lens unmounted, pushing this button will close the aperture.

As for selling it, I hope ~€1 will come in handy. An aftermarket OM lens has essentially no value.

 

[Les Sarile]

An aftermarket OM lens has essentially no value.

Of course really broad statements don't necessarily apply all the time . . .

 

[albada]

You can determine whether the aperture is stuck as follows:

1. Set the f-stop to f/16.
2. Press both of the tabs on the mounting ring. As others have said, one is the release, and the other is depth-of-field preview.
3. Looking through the lens, and you should see the aperture close down while pressing those tabs inward.

My collimator-test showed that this lens is sharper than most in its class, so it should be a good performer (assuming the aperture isn't stuck).

Mark Overton

 

[mhofmeist]

Thank you very much to all who answered so quickly.

It is as I feared - the diaphragm does not move whatever I do, following your helpful instructions.

Anyone willing to try a repair? Otherwise I will have a go at it myself. Not for financial reasons, I just think the lens is worth it.

 

[Sean Mac]

My favourite aftermarket OM lens

Sigma 70/210 F2.8 Apo.

Apologies for phone picture...I don't have a better electronic camera

 

[wblynch]

The Tokina 35-105 is a fabulous lens for the OM film cameras. In fact it was repackaged as the Zuiko 35-105 lens for Olympus factory offering. I have one of each and my Tokina actually has a better coating system.


Before you monkey with it, try getting an OM body and using the lens.

Although not highly valuable, it would be a shame to have such a nice lens go to waste.

 

[Fixcinater]

I'm on the other side of the pond, otherwise I'd offer to take a look.

You may be able to get the rear group out and get at the aperture easily to clean it of it's oil which is likely the cause of your trouble. I don't know the design at all, but it may be entirely accessible and straight-forward.

It also may be a royal PITA to get at it.