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02-17-2012, 10:10 PM   #1
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M42 105mm 2.8

Hi there ladies and gents. I have an issue with a lens I recently acquired. It was working fine earlier today I switched the aperture to get a sharper pic.....boy was it sharp at 5.6.

There is a little lever on the side that I slid down and the aperture returned to wide open again regardless of the aperture i set it on. At this point I was puzzled and removed the lens and pressed the little pin like deal on the back. and it returned to 5.6 after a while I started shooting some stuff with lighting and moved the aperture to f16 and while focusing to get a sharper image I moved that little.....lever again, at this point I shut down the cam and pressed the pin again and it made the sound like it was returning the aperture to normal but it stayed wide open........Any clues on what could be wrong?

I am sure that was a tough read for some of you guys but I have no idea how to really describe this incident. Any help will be greatly appreciated

02-17-2012, 11:04 PM   #2
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There are several variants of the M42 105mm, the one you have sounds like the Auto-Takumar 105 f/2.8. If so the little lever is (was) used to reset the aperture after taking a shot. The earlier Takumar variant was a preset lens with two aperture rings, you set one to the aperture you wanted, focused, and then turned the other aperture ring to close the aperture to take the shot. The Auto-Takumar allowed the camera to close the aperture just before taking a picture instead of you having to turn the ring manually, which allowed you to focus wide open and then take the shot. The little lever was then used to "re-cock" the lens for the next shot.

Of course this only worked on the cameras that were made to function with this lens. The mechanism will not work with new cameras as they have no linkage to actuate the lens. Later variants such as the Super-Takumar and the S-M-C Takumar did away with the lever and the lens was actuated by the camera without having to "re-cock" the lens. On today's camera these lenses must be used in manual (or Av) mode and the aperture ring turned manually.

Here is a link to the Auto-Takumar 105mm, if this isn't the lens you have then post a picture or the exact description and I'm sure someone can help.
02-17-2012, 11:06 PM   #3
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For the lens to work with your camera, you should leave the switch in manual. Is it stuck now? This might help:

https://www.pentaxforums.com/forums/maintenance-repair-articles/3954-why-auto...heres-pin.html

And this also:
https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-meter...k-x-k-7-a.html

Adam
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02-18-2012, 01:21 PM   #4
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Aperture pin

Hi there guys thank you for getting back to me. I have the exact lens that you listed jatrax. I looked all over this thing and didn't see the other pin. I got frustrated with it and pulled the mounting plate off of there and I see that the lever/knob moves about just right but the aperture stays fixed on what ever I set it to with the mounting plate off of there. I am going to leave it at 5.6 for now. Something isnt connecting properly back here and I will have to get brave enough to finish this job.

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