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12-01-2011, 08:38 AM   #1
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50mm f 1.7 stuck aperture ring

I recently inherited a pentax program plus with a 50mm f 1.7 lens. I'd like to start using it but the aperture ring is stuck at f/8. What is the problem? Are there any home remedies I can do to fix this or should I just take it to a professional?

Also, is there a difference between the pentax K mount and the KA mount. I'm thinkin about buying an adapter for this lens for my t2i but can only find the K mount for this KA mount camera.

12-01-2011, 08:46 AM   #2
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QuoteOriginally posted by Nino123 Quote
I recently inherited a pentax program plus with a 50mm f 1.7 lens. I'd like to start using it but the aperture ring is stuck at f/8. What is the problem? Are there any home remedies I can do to fix this or should I just take it to a professional?

Also, is there a difference between the pentax K mount and the KA mount. I'm thinkin about buying an adapter for this lens for my t2i but can only find the K mount for this KA mount camera.
Aperture ring stuck is usually caused by oil on blades. You would have to dismantle the lens and clean the aperture blades. Use Google for instructions.

K is all manual, KA has a pin that sends the selected aperture to the camera body. This is useful when shoot with Aperture priority mode.
12-01-2011, 08:57 AM   #3
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While stuck aperture blades indeed require opening the lens, a stuck aperture ring might not. I had an M50/1.7 with that problem, which I fixed without opening anything.

I used some kind of solvent, probably not lighter fluid but something similar and applied it with some tissue paper where the aperture ring meets the lens body, let it sit for a while, applied it agian, and then used quite a lot of force to move the ring. Applied some more solvent and worked the ring, and it was a little rough but perfectly useable afterwards.

Edit: Also, M lenses send the selected aperture to the body too, the A lenses allow the body to control the aperture, which is a different thing. It makes no difference if you're using it on an adapter.
12-01-2011, 09:28 AM   #4
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QuoteOriginally posted by ducdao Quote
Aperture ring stuck is usually caused by oil on blades. You would have to dismantle the lens and clean the aperture blades. Use Google for instructions.

K is all manual, KA has a pin that sends the selected aperture to the camera body. This is useful when shoot with Aperture priority mode.

ok, but as far as the mount, they are the same?

12-01-2011, 09:32 AM   #5
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QuoteOriginally posted by Nino123 Quote
ok, but as far as the mount, they are the same?
Yep, same mount.
12-01-2011, 10:21 AM   #6
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The suggestions so far are good for a Pentax-M 50mm f1.7. The Pentax-A 50mm f1.7 is more likely to have a different problem causing a stuck ring. The repair is covered here:

https://www.pentaxforums.com/forums/maintenance-repair-articles/88051-pentax-...ng-repair.html
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