Matthew Sovern , Sep 04, 2010; 07:50 p.m.
(edit) I'm using a Canon AE-1 Program
Just received my Soligor 75-205mm "FD-mount" lens. The "bayonet" is similar to the normal FD mount lenses that I own but seems to be stopping the mirror from completing a full exposure. The only way I can take a full exposure is if I press in the "stop-down lever" (which is used for metering). Below is a picture of the mount.
(Below) is a normal Vivitar 28mm FD mount lens. This lens has the usual "bayonet."
Am I missing something. Is that 75-205 not an FD mount or do I need some sort of extension. Help!
Matthew Sovern , Sep 04, 2010; 08:38 p.m.
Dave Sims 
, Sep 04, 2010; 08:46 p.m.
Matthew, welcome to photo.net. I believe the spring in the aperture mechanism is too stiff, so your camera is not strong enough to overcome it.
The stiff spring prevents the automatic aperture from stopping down completely. The aperture must be stopped down (and the mirror up) before the camera will open the shutter. Because of that, a stiff spring shuts everything down, before the exposure is made. Having said that, the lens may work on a different camera body.
If you look at your pictures, the lever at the top is the one the camera uses to close the iris diaphragm to the selected aperture. In your picture of the Soligor, it is the crude rectangular switch. If you try to move that lever counter-clockwise, you will feel the spring tension is greater on your Soligor than on your Vivitar.
I think this is fairly common with third-party lenses. I've had it happen with a couple of lenses (both actually FL rather than FD). FWIW, one of them was a Soligor 400/6.3 I had 30 years ago, which had an interchangeable 'T' mount. In that case, it was just a matter of replacing the mount, to one with less spring tension. The other lens was a Novoflex 100mm bellows lens; I sent it back.
Matthew Sovern , Sep 04, 2010; 08:57 p.m.
Any way to "wear out" the spring? I think your right. The spring is stronger than my 28mm spring.
Dave Sims , Sep 04, 2010; 09:18 p.m.
Any way to "wear out" the spring?
I don't know, but I don't think so. I bet the spring will keep the same tension until someday it justs breaks and fails, after a few hundred thousand cycles. But I don't know anything about materials or springs.
Having a technician overhaul the lens might help, but in this case, forget it-- the cost would greatly exceed the value of this lens.
If I were you, and I'm not, I'd use it as a 'preset' lens, which is what you're doing. Meter at full aperture, because you can, and then close the diaphragm manually just before you trip the shutter. It will slow you down just a bit, but not much.
Save a few bucks for a replacement, maybe the Canon FD equivalent. If you have a few more bucks, like $250, look for an FD 80-200/4 L lens, which people here say is the best FD zoom ever made.
Matthew Sovern , Sep 04, 2010; 09:34 p.m.
What does that lens, in good condition, usually run? I really new to acquiring new gear. I've had the same gear since I've started, until now.
Dave Sims , Sep 04, 2010; 09:44 p.m.
Check KEH.com prices, or ebay completed auctions. KEH is a better idea if you live in North America.
I'm not really a zoom kind of guy, don't know the Canon FD zooms. I think the non-'L' ordinary Canon FD 70-210, or whatever the heck it was, was a popular lens. This means there's a lot of them out there, so prices should be favorable. I don't know whether it's a good lens, so do some research.
