Olympus OM-2000 sticking mirror

Matt Friedman · Nov 24, 2017

I know the OM-2000 isn't a REAL Olympus (it is so obviously a Cosina that, if it had a K-mount, it's be a Ricoh), but I was wondering if anyone knows how to fix a sticking mirror.

The issue: When I press the shutter button, the shutter clicks, and the mirror stays up. This does not happen all of the time, and the mirror drops down with a little shake, or by moving the aperture ring. And it happens mostly with a Zuiko 50mm f/1.8 lens, and less (though occasionally) with a Tamron zoom lens with the Adaptall-2 OM mount adapter.

I suspect this is either a gear that needs to be lubed, or a sticking bumper, but before I start poking around inside, I'd wouldn't mind having an idea of what to look for.

I'm mostly a Minolta and Pentax guy (no disrespect to Olympus; I have an investment in glass), and I've solved this problem before on SRTs. This is my only Olympus; part of my collection for students.

john.margetts · Nov 25, 2017

That is almost certainly the foam buffer deteriorating to sticky goo. Very easy to remove the old foam from the edge of the focus screen being careful not to get any on the actual screen. New foam can be bought from any hobby shop - self adhesive version, of course.

The camera is, as you say, a Cosina. A Cosina CT1 Super, to be precise. Also known as a Nikon FM10 and Canon T60. An excellent camera.

Matt Friedman · Nov 25, 2017

Thanks! I'll poke around with it when I have shot off the roll.

I actually rather like the Cosinas from the 90s. They're bare-bones cameras, but they make great student cameras. The light meter display is perfect for beginners, and the advance-lever lockout is great to prevent misfires. I often think of buying up a bunch of them for teaching.

Matt Friedman · Nov 30, 2017

After shooting off the roll, it's clear that the mirror only sticks consistently with the Zuiko 50mm f/1.8 kit lens at f/11-f/16. It appears that, when the tab rotates to the right on the aperture ring, it prevents the mirror from dropping completely. So... How can I remedy this problem? I suspect it is related to using an older Zuiko lens on an outsourced Olympus body, but I also suspect that I am not the only person ever to encounter the issue.

jcdeboever · Nov 30, 2017

https://www.google.com/url?sa=t&sou...sDoMQFggoMAA&usg=AOvVaw0kWyTOoDA_1UmP4uxy2FAN

Matt Friedman · Nov 30, 2017

jcdeboever said:
https://www.google.com/url?sa=t&sou...sDoMQFggoMAA&usg=AOvVaw0kWyTOoDA_1UmP4uxy2FAN

Thanks for this... But I have to ask: If the problem IS the damper, then why does this only happen on the 50mm lens, and only at f/11-f/16? I'm not trying to be difficult (or ungrateful for the link), but I am trying to understand. Since, if the problem was the damper, wouldn't that mean that the problem would occur all the time, on any lens?

jcdeboever · Nov 30, 2017

Matt Friedman said:
jcdeboever said:

https://www.google.com/url?sa=t&sou...sDoMQFggoMAA&usg=AOvVaw0kWyTOoDA_1UmP4uxy2FAN

Click to expand...

Thanks for this... But I have to ask: If the problem IS the damper, then why does this only happen on the 50mm lens, and only at f/11-f/16? I'm not trying to be difficult (or ungrateful for the link), but I am trying to understand. Since, if the problem was the damper, wouldn't that mean that the problem would occur all the time, on any lens?

Not necessarily, it has been my experience that sticking mirrors are not always consistent. Not sure why but I had a Pentax K1000 that did that, and replacing the mirror bumper did the trick. It was a gooey mess. You can check it easy enough by touching, slight rubbing the foam if any is left, if it is tacky, replace it. It will transfer some black to your finger, be careful about touching the mirror. If the foam seems it's in good order, which I doubt, it may be something mechanical.

Matt Friedman · Nov 30, 2017

It isn't the damper. It's dry and spongy, and not tacky at all... It does seem to relate to the lens and mount, however. The mirror never sticks with no lens. It only sticks when a lens is attached and stopped to f/11 or f/16. It sticks on BOTH of the lenses that I have with OM mounts. (I didn't THINK it stuck on the Tamron, but that was only because its sweet spot is f/8, and I didn't use it on the OM2000 at f/11 or f/16. I have since confirmed that it sticks.) Significantly, the mirror does NOT stick when the Tamron is at f/22.

This suggests that the problem is (a) some kind of mechanical obstruction, and (2) it is variable, only catching the mirror at certain parts of the arch of the lens mount circle. And really the ONLY culprit in this case -- the only thing can CAN be obstructed at the arc of the lens mount circle -- is the aperture tab.

So... I have to wonder if other OM2000 users have encountered this issue and, if so, how did you resolve it? I'll develop the test roll later today, to see if that gives me any hints.

Thanks to all who have helped, and thanks in advance to anyone who can continue to shed light on this.

john.margetts · Nov 30, 2017

When you change the aperture on the lens aperture ring, the lens mount linkage turns a ring just inside the throat of the mount on the camera side. The amount this ring turns by is determined by the aperture setting. Your mirror is clearly fouling this ring when the linkage is at a certain point. I would suggest that the locating lug on this ring has got slightly bent so that the mirror is just touching it at f/11, stopping it freely moving.

Matt Friedman · Nov 30, 2017

So... There's a spring-loaded coupling ring just behind the outer ring plate on the camera body, and there seems to be a tab at about 10:00 (where the red lens alignment dot is) when it is at rest. Is this what you are talking about?

john.margetts · Dec 1, 2017

Yes.

It is hard to really know without having the camera in my hgands, but this is the only aperture sensitive part near the mirror.

Matt Friedman · Dec 1, 2017

john.margetts said:
Yes.

It is hard to really know without having the camera in my hgands, but this is the only aperture sensitive part near the mirror.

Yup. That's it.

So... I'm at a bit of a loss as to how to fix this. The obstruction seems to amount to about 0.5mm. The obvious solution would be to bend the lug a tiny bit to clear the mirror, but I am hesitant to do this. Should I disassemble the coupling mechanism, or do you think it would be safe to gently reach in with needle-nose pliers?

john.margetts · Dec 2, 2017

I've wrecked that many cameras doing simple repairs, I'm not the one to give advice here.

The potential problem with bending the tab in situ is that you might bend the ring as well. Sorry, I can't really advise you.

Matt Friedman · Dec 2, 2017

I quite understand. The issue here is that, as it is, this camera is unusable for teaching, and I wouldn't sell it, knowing that it has this annoying fault. So it's worthless as it is. Moreover, it cost me nothing, and I have several other SLRs that I use on a daily basis.

So I don't really hurt myself by attempting a repair, even if it fails.

Having said that, it occurs to me that the best solution would be to buy a dead Olympus for parts, and just use the ring from that. So... I wonder, is the OM mount mechanism constant throughout the line? That is, would parts from an another model be compatible with the mounting mechanism in the OM2000?

I've looked at the OM2000 service manual, and it doesn't look like replacing the ring would be that difficult (assuming I can load the spring properly). So that might be the best option, assuming I can get the part inexpensively. (I don't want to sink more than $10 into this camera.)

john.margetts · Dec 2, 2017

The Olympus lens mount has to communicate with the Cosina light meter and other internals. That might mean that the detail of the ring is different .from what an Olympus part would be. Or it might not be.