OM Zuiko 50mm 1.4 aperture not closing

[mnemosyne]

A n older "silvernose" 50mm 1.4 Zuiko has found its way to me. The lens is overall in nice shape, but the aperture won't stop down.

When pressing the DOF preview button on the lens, one time out of ten the aperture will close halfway, the rest of the time it will just not react and stay wide open. When attached to a camera, the aperture does not stop down at all when firing. The aperture ring moves freely as it should with normal click stops.

This is not the common "sticky aperture" problem, as the aperture blades move swiftly when they move.

Do you have any ideas what part of the aperture mechanism might be at fault here and how to get best access to it?

 

[AgX]

You got sticky apertures, where the leaves are obviously oily and move slow at all instances.
But there are also sticky apertures where there is no oil or anything visible on the leaves. Here the stickiness is caused at their pivoting, the twisting ring that actuates the leaves or even further off. In cases I "repaired" such lenses by countless times pressing the lens' actuator. But I assume the best way even with leaves working correctly again is to disassemble the lens and have a look at that ring.

 

[Arbitrarium]

I had a slow aperture on one of these and found out it had nothing to do with the blades, but the linkage near the rear of the lens. The back comes off with a couple of screws and the linkage is right there, you can remove it very easily and give it a good clean, then replace it. Worked for me, and was the most painless lens repair I've ever had.

 

[EdSawyer]

Yes, look for the parts diagrams online, the rear mount comes off with 3 screws, it should be easy to check the linkage at that point.

 

[colin wells]

Arbrtrarium and EdSayer have it spot on there's a how to on youtube

 

[mnemosyne]

Okay, I pulled the mount and what I found is that there seems to be a problem with the linkage between the auto aperture lever in the mount and the pin that protrudes from the iris assembly towards the mount. When I operate that pin with a screwdriver, the blades will close and snap open just fine, no problem. So the aperture mechanism itself is sound, but something in the linkage doesn't line up. On closer inspection the pin that comes from the aperture assembly looks a bit crooked/bent to me, but maybe that's how it's supposed to look. Unfortunately the pin in question is difficult to photograph. I tried to reassemble the mount, which was not easily possible, again a sign that something may be bent or crooked. I will try again tomorrow.

 

[BMbikerider]

Older Zuiko lenses have a reputation of having 'lazy' diaphragms. Usually congealed lubricant. They rely upon a an internal spring to close the aperture, whilst other lenses such as those made by Nikon the lens is closed down positively - in other words it is forced. The other side is when the closing down lever is released the blades open slowly.
A good clean is all that is needed

 

[mnemosyne]

Thank you to all for your input, problem is solved. It was not related to the sticky aperture syndrome. The perpendicular linkage between the aperture lever in the mount and the pin that is attached to the actual iris had simply become separated for reasons unknown. Contrary to my first thoughts, the pins were not bent. After removing the smaller flat black painted inner ring at the back of the lens mount, I was able to reattach both pins easily and now the aperture is working flawlessly

 

[EdSawyer]

nice! Well done. The zuikos are not too hard to work on, I have repaired several and opened up many of them to give them full cleanings (esp in the centers where the aperture is, to remove dust/oil/etc.).

 

[mnemosyne]

nice! Well done. The zuikos are not too hard to work on, I have repaired several and opened up many of them to give them full cleanings (esp in the centers where the aperture is, to remove dust/oil/etc.).

My rejoicing was premature ... The problem is back. Midway through the first roll, the aperture suddenly stopped working (closing). Disassembled the mount and found the linkage hat disconnected again. Reconnected it carefully, but the problem keeps coming back after firing the shutter for 20 or 30 times, the aperture stops working ...

 

[EdSawyer]

pics would help...

 

[shutterfinger]

Sounds like the pin is slipping out of socket. With the pin in place try crimping the socket slightly with needle nose pliers or retain the pin with JB Weld or similar, only a small dab on the open end of the socket will be necessary.