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07-23-2016, 02:02 PM   #1
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M42 mount won't tighten

Hi all! New to the forum. I found an Asahi Super Multi Coated Takumar 35mm f3.5 at a pawn shop for $10. Amazing deal right?? So I go to put it on my Mamiya 1000 DTL, and it screws in all the way, and is not looks in the mount or anything, but it just won't stay tight. It wants to turn with the aperture and focus rings. It's like there's no tension when tightening like normal lens when you can feel it getting tighter, it just stops and feels like it will loosen very easily. Also the numbers land 90 degrees on the lens, not at the top like normal. Anyone know why this is? Thanks!

07-23-2016, 02:38 PM   #2
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Just to clear things up. Other m42 lenses screw onto the camera normally? And can you maybe try that lens on another m42 camera or adapter? Just to pinpoint whether the problem is on the lens or camera mount.
Anyway, inspect the mount. m42 is mechanical, so just look for faults in the screw threads. Maybe there is a problem there. Don't use too much force, though, as forcing things can lead to problems
07-23-2016, 03:17 PM   #3
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There are some screw mount lens like that... the base plate is not flat and flush with the lens mount (a small circular step towards the center). You can use a piece of aluminum foil as shim before you tighten the screw mount. That should fix the problem.
07-23-2016, 03:35 PM - 1 Like   #4
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Concur with aleon re shim.

Check it as is first - if it focuses beyond infinity shims are needed anyway.

I'd try cellophane tape or black electrician's tape. Being sticky is a convenience! And they offer two different thicknesses of shim. Too much shim will act as a thin extension ring and prevent infinity focus.

Do balance the shims around the mount to prevent 'tilting' in the mount.

The 'right' amount of shim will probably center the aperture index as well.

07-23-2016, 04:27 PM   #5
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QuoteOriginally posted by Dhuiting Quote
Hi all! New to the forum. I found an Asahi Super Multi Coated Takumar 35mm f3.5 at a pawn shop for $10. Amazing deal right?? So I go to put it on my Mamiya 1000 DTL, and it screws in all the way, and is not looks in the mount or anything, but it just won't stay tight. It wants to turn with the aperture and focus rings. It's like there's no tension when tightening like normal lens when you can feel it getting tighter, it just stops and feels like it will loosen very easily. Also the numbers land 90 degrees on the lens, not at the top like normal. Anyone know why this is? Thanks!
Welcome to the Pentax Forums!

The lens and camera should be fundamentally compatible and your SMC Tak 35/3.5 should snug up with normal tension. There is a small pin that is unique to SMC lenses that extends to the mount face. The pin is part of a mechanical interlock used for open-aperture metering with compatible bodies. Is there any chance that that pin is jammed such that the lens will not fully snug down onto the mount?


Steve
07-23-2016, 04:41 PM   #6
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QuoteOriginally posted by stevebrot Quote
The pin is part of a mechanical interlock used for open-aperture metering with compatible bodies.
The pin is retracted when the Man/Auto switch is in the "Man" position and will be extended when in the "Auto" position. When the pin is extended the Man/Auto slider switch barrel will be "locked" in the "Auto" position. This is by design and the switch should not be forced.


Steve
07-23-2016, 06:17 PM   #7
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QuoteOriginally posted by Dhuiting Quote
Hi all! New to the forum. I found an Asahi Super Multi Coated Takumar 35mm f3.5 at a pawn shop for $10. Amazing deal right?? So I go to put it on my Mamiya 1000 DTL, and it screws in all the way, and is not looks in the mount or anything, but it just won't stay tight. It wants to turn with the aperture and focus rings. It's like there's no tension when tightening like normal lens when you can feel it getting tighter, it just stops and feels like it will loosen very easily. Also the numbers land 90 degrees on the lens, not at the top like normal. Anyone know why this is? Thanks!
Are you using an adapter to make this lens work with your camera?

07-23-2016, 08:32 PM   #8
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QuoteOriginally posted by reh321 Quote
Are you using an adapter to make this lens work with your camera?
No adapter is needed to the Mamiya 1000 DTL mentioned in the original post.


Steve
07-24-2016, 03:26 AM   #9
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Lots of help already given, so I'll just say welcome.
07-24-2016, 09:44 AM   #10
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QuoteOriginally posted by Kerrowdown Quote
Lots of help already given, so I'll just say welcome.
Thank you all so much! Very helpful and quick responses.

To answer the questions:

Na Horuk: It is definitely something with the lens. Other lenses screw on to my camera just fine, and the lens in question has the same problem when I screw it onto my Mamiya 500 DTL (I have two of them, same problem on all cameras I try this lens on.)

Pacerr: Thanks! I tried electrical tape (1 layer thickness wasn't enough, but 2 layers worked!) I put 4 groups of two, one group at each side (North, East, South, West if you're looking down at the rear of the lens) and that seems to keep the lens in place.

Stevebrot: The manual/auto switch will only work when the lens is on the camera, so I can't look at the rear of the lens and see whether the pin retracts or not while moving the lever from "A" to "M" but I tired taking the lens off both in M and A mode, and the pin sticks out in both. But if I push my finger in the pin it pushes in quite easily.

Reh321, as Stevebrot mentioned, there is no adapter, the lens screws right into the camera.

Thanks everyone for the timely and thoughtful replies, I believe this problem is solved!
07-24-2016, 12:09 PM   #11
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There's about a 2mm 'gap' between the base of the M42 lens and the beginning of the threads that may be somewhat incompatible with the Mamiya mount.

A more secure option would be to use a suitably thin, soft rubber O-ring or rubber band as a shim - diameter about 1-5/8ths in / 38-40mm should work. A trial fit available in most good hardware stores (ie, Lowes, USA?). The soft 'shim' should allow the lens to snug up nicely with little or no extension tube effect on focusing range. May even add a bit of WR protection for the mount.

(Including a clue as to your location in personal info helps folks suggest resources for shopping and repairs.)
07-25-2016, 11:16 AM   #12
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QuoteOriginally posted by pacerr Quote
There's about a 2mm 'gap' between the base of the M42 lens and the beginning of the threads that may be somewhat incompatible with the Mamiya mount.

A more secure option would be to use a suitably thin, soft rubber O-ring or rubber band as a shim - diameter about 1-5/8ths in / 38-40mm should work. A trial fit available in most good hardware stores (ie, Lowes, USA?). The soft 'shim' should allow the lens to snug up nicely with little or no extension tube effect on focusing range. May even add a bit of WR protection for the mount.

(Including a clue as to your location in personal info helps folks suggest resources for shopping and repairs.)
Thanks Pacerr, although it is less permanent, the electrical tape is working great for me so far. Also I updated my profile, thanks for the tip. Cheers guys. Problem solved
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