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Need Advice Fixing Diaphragm Pentax Super Takumar 50mm 1.4
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PostPosted: Sat May 12, 2018 6:05 pm    Post subject: Need Advice Fixing Diaphragm Pentax Super Takumar 50mm 1.4 Reply with quote
Super Takumar 50 1.4 When pushing a stop-down pin on the rear of the lens, the diaphragm would close down but when letting the pin go the diaphragm would stay closed. It won't bounce back to wide open position. The lever is switched to AUTO. Took it apart looked at diaphragm mechanism all looks OK, but I may be missing something. I am not familiar with this lens. Maybe a part is missing or a spring is out of place? Would appreciate any ideas. What is the mechanism moving diaphragm to close and back to open? Diaphragm blades move freely and easy.

Not sure why pictures aren't attaching, but I put few photos of diaphragm lever on my drive. https://drive.google.com/drive/folders/1ufQ1HAfjtbxx3bCFzKoWEuKdFlyXESGD?usp=sharing










PostPosted: Sat May 12, 2018 6:36 pm    Post subject: Re: Need Advice Fixing Diaphragm Pentax Super Takumar 50mm 1 Reply with quote
CameraCravings wrote:
Super Takumar 50 1.4 When pushing a stop-down pin on the rear of the lens, the diaphragm would close down but when letting the pin go the diaphragm would stay closed. It won't bounce back to wide open position. The lever is switched to AUTO. Took it apart looked at diaphragm mechanism all looks OK, but I may be missing something. I am not familiar with this lens. Maybe a part is missing or a spring is out of place? Would appreciate any ideas. What is the mechanism moving diaphragm to close and back to open? Diaphragm blades move freely and easy.

Not sure why pictures aren't attaching, but I put few photos of diaphragm lever on my drive. https://drive.google.com/drive/folders/1ufQ1HAfjtbxx3bCFzKoWEuKdFlyXESGD?usp=sharing










PostPosted: Sat May 12, 2018 7:08 pm    Post subject: Re: Need Advice Fixing Diaphragm Pentax Super Takumar 50mm 1 Reply with quote
Thanks for this!!

So the diaphragm moving lever with a fork (seen in picture 4 and 5) is not tensioned unless the pin on the back of the lens is pushed in. If the pin is pushed in the lever is tensioned both ways. If the pin is released the lever is not tensioned at all in either direction. This is why the diaphragm does not return to open. I am wondering if a spring is missing somewhere. It does not look like the lens had been repaired or opened before.

However the normal operation of the camera includes: 1 the lens aperture is wide open; 2 shutter release button on the camera is depressed; 3 stop down lever intermittently pushes in the pin on the back of the lens and diaphragm closes; 4 the pin returns to its original position and diaphragm opens. Whith my lens this is not the case.

At this point I feel I should buy another ST 50 1.4 open it up and compare...

Thanks for any suggestions!!


PostPosted: Sat May 12, 2018 7:45 pm    Post subject: Reply with quote
I think I,m right in saying,you need the Aperture ring set to max closed (f16 f22 etc) to get maximum movement of the actuating arm.What makes you think it isnt the aperture itself thats sticking?


PostPosted: Sat May 12, 2018 10:09 pm    Post subject: Reply with quote
When I am holding lens pack in my hand and moving aperture lever aperture blades move freely without sticking.

Eddie46 wrote:
I think I,m right in saying,you need the Aperture ring set to max closed (f16 f22 etc) to get maximum movement of the actuating arm.What makes you think it isnt the aperture itself thats sticking?
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