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11-16-2017, 12:11 PM   #1
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What are normal stopdown preset mechanics for M42 Takumars?

I just bought a screwmount lens, a Super-Multi-Coated TAKUMAR 1:1.8/85, my first M42 lens.

Problem 1: The preset ring is JAMMED, stuck in the AUTO position.

The aperture ring turns ok, and it stops the blades stop down appropriately, but only when the small silver control pin on the back of the lens is depressed into the lens body. I take this as normal.

Problem 2: However, as the aperture ring is turned the aperture lever at the back of the lens also moves back and forth in its slot, but does so RIGIDLY. This differs from the rear aperture stopdown levers in "modern" (K and later) lenses which also move when the aperture ring is turned, but are sprung so that slight finger-force can push the lever to the stopdown position and close the blades. The fixed lever-position behavior in this Takumar might be normal for all I know, but I'm reluctant to put it on my camera to find out, lest the camera internals damage themselves trying to move something that should but won't.

Instead of just sending the lens back as dysfunctional, I'm thinking of trying to negotiate some kind of a discount that will cover the cost of a repair. (The glass looks clear, with the slight yellow tinge.) But I first want to be sure that my concerns are well-founded, and not just a newbie's misinterpretation of normal operation.

I'd be very grateful if someone with an operational Takumar could compare notes.

Thanks much - Gerry

11-16-2017, 12:22 PM - 1 Like   #2
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A few misunderstandings:

  • S-M-C Takumars have a small silver pin on the bottom of the mount, nearly opposite the auto/manual switch, (much smaller than the one to close down the aperture) that has to be pushed in for you to be able to switch to manual. If the lens is mounted on most bodies, this is pressed, and you can easily switch. This is unique to S-M-C and SMC Takumar lenses.
  • There isn't a lever that opens the aperture like on the K-mount. The aperture is open by default in auto mode, and the little silver pin closes down the aperture.
  • In manual mode, the little silver pin does nothing, and the aperture opens and closes based on the position of the aperture ring.


In short, it doesn't sound like the lens has any issues.

Last edited by timw4mail; 11-16-2017 at 12:23 PM. Reason: More clarification
11-16-2017, 12:34 PM - 1 Like   #3
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It sounds normal. Just depress the small pin. You can find some pictures in this other thread:
SMC Takumar 55/1.8 Odd pin. - PentaxForums.com
11-16-2017, 12:36 PM   #4
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#1. There is no preset ring on that lens. If you mean the Auto / Man switch yes that is normal it does not move unless mounted to the camera or the pin depressed by hand.

#2. There is no aperture connection to k-mount cameras from an M-42 lens. The lever you see was for M-42 cameras. Just ignore it, it has no function on k-mount.

In short, nothing wrong with the lens, working as designed.

Have you read through this: Using Manual Lenses (M42 Screwmount, M , K) on Pentax DSLRs F-- - PentaxForums.com

11-16-2017, 01:33 PM - 1 Like   #5
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Very happy ending! Thanks, especially Tim!

When I first saw Tim's reply, I thought we were talking at odds. Trouble is, there are TWO silver pins, the big one that I had referred to, and the tiny one recessed in the lens mount that Tim talked about that frees the AUTO/MAN switch. I didn't find it at first, but I cautiously screwed the lens onto the camera, and to my amazement the AUTO/MAN switch, and the lens itself, worked just as Tim said. After taking the lens off, I discovered the tiny pin by noting that screwing the M42 adapter on was enough to free the AUTO/MAN switch, but only when the adapter was nearly tight. Thanks, sergysergy, for your link showing the picture.

I suppose the lever that the aperture ring moves in the slot in this Takumar was only designed to tell the (film) cameras the aperture settings, unlike the lever in later cameras that additionally had a stop-down function.

Also, although admittedly not designed for this purpose (like an actual preset ring on say, the 28mm shift lens), you can sort of use the AUTO/MAN switch as a preset: choose your aperture with the ring, then switch to AUTO to focus, and then to MAN to stop down to meter with the green button.

Finally, I HAD found Adam's article, and in fact had found it very helpful previously when trying to set up catch-in-focus for manual lenses. There were many other similarly helpful descriptions on how to set up the camera, but I had a hard time finding much about mechanical interlocking and functionality of the lens by itself.

So thanks very much for your replies; you saved me major embarrassment!
11-16-2017, 04:45 PM - 1 Like   #6
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QuoteOriginally posted by eyeball Quote
Also, although admittedly not designed for this purpose (like an actual preset ring on say, the 28mm shift lens), you can sort of use the AUTO/MAN switch as a preset: choose your aperture with the ring, then switch to AUTO to focus, and then to MAN to stop down to meter with the green button.
If you use Av mode, you don't have to use the green button to meter. The camera should meter automatically. I'm referring specifically to M42 lenses here. The aperture stops down as soon as you move the slider to MAN.
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