M42 to K-mount adapter won’t unscrew

estost · 04-07-2022, 07:46 AM

Originally posted by photogem

That's exactly how I do it with many of my Takumars and other M42 lenses (pin down so one can use the aperture ring)
but a slightly different way:

1. Take the spring on the adapter off, bring the adapter very tight onto the M42 lens (I built myself a tool with the K-bajonett of a defunct Pentax)
2. The tiny screw which held this spring might go deep enough into the thread, if not use a slightly longer one. This will hold the adapter tight as well.
(or one can use thread-locking-laquer which won't damage the M42 thread)

This will position your lens different on your Pentax, but so what! It works very well, I have done so since ages and I use the cheap chinese adapter as well like this. Only my favourite Takumars and a Zeiss got the orig. Pentax Adapters.
There were 3-rd party adapters machined quite well such as Hama.

If one knows one will keep the lens and doesn't worry about modifying it, this method works great:

1. Insert the M42 adapter.
2. Mark that part of the bajonett which will lock the lens with a marker-pen (red arrow):

3. Keep the lens-unlock-button pushed in and mount the M42 lens
4. Let go of the lens-unlock-button and wait for 2 seconds (you might have to repeat that a few times though)
5. Unscrew the M42 lens, you know should see a round mark on your bajonett
6. Exactly in the middle of that hole punch a precise mark (with a center puncher and a soft hit with a small hammer)
7. Drill a 1mm hole there, then a 2,2 mm hole 2,5mm deep (some lenses are thinner there, but most have about 5mm)

This locks your lens now exactly at that point so the lenslocker can slip in.

You have to work very precise and a precision drill on a stand is almost obligatory.

Thanks a lot, photogem, for writing down the process!

I did it with two Mayer Görlitz lenses and it was really worth it. With more ancient M42-lenses with a conical backend you will however need a flanged adapter, that way losing infinity. But even that is not a big problem: Take the backend apart and take it to a metal shop. They will find a way to turn down one of the rings on the lathe to make up for the flange thickness. I think in my case they simply enlarged the space behind the threads enabling the adapter ring to screw on further.

Last edited by estost; 04-07-2022 at 08:22 AM.

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04-07-2022, 07:46 AM	#16
estost Junior Member Join Date: May 2016 Photos: Gallery Posts: 33	Originally posted by photogem That's exactly how I do it with many of my Takumars and other M42 lenses (pin down so one can use the aperture ring) but a slightly different way: 1. Take the spring on the adapter off, bring the adapter very tight onto the M42 lens (I built myself a tool with the K-bajonett of a defunct Pentax) 2. The tiny screw which held this spring might go deep enough into the thread, if not use a slightly longer one. This will hold the adapter tight as well. (or one can use thread-locking-laquer which won't damage the M42 thread) This will position your lens different on your Pentax, but so what! It works very well, I have done so since ages and I use the cheap chinese adapter as well like this. Only my favourite Takumars and a Zeiss got the orig. Pentax Adapters. There were 3-rd party adapters machined quite well such as Hama. If one knows one will keep the lens and doesn't worry about modifying it, this method works great: 1. Insert the M42 adapter. 2. Mark that part of the bajonett which will lock the lens with a marker-pen (red arrow): 3. Keep the lens-unlock-button pushed in and mount the M42 lens 4. Let go of the lens-unlock-button and wait for 2 seconds (you might have to repeat that a few times though) 5. Unscrew the M42 lens, you know should see a round mark on your bajonett 6. Exactly in the middle of that hole punch a precise mark (with a center puncher and a soft hit with a small hammer) 7. Drill a 1mm hole there, then a 2,2 mm hole 2,5mm deep (some lenses are thinner there, but most have about 5mm) This locks your lens now exactly at that point so the lenslocker can slip in. You have to work very precise and a precision drill on a stand is almost obligatory. Thanks a lot, photogem, for writing down the process! I did it with two Mayer Görlitz lenses and it was really worth it. With more ancient M42-lenses with a conical backend you will however need a flanged adapter, that way losing infinity. But even that is not a big problem: Take the backend apart and take it to a metal shop. They will find a way to turn down one of the rings on the lathe to make up for the flange thickness. I think in my case they simply enlarged the space behind the threads enabling the adapter ring to screw on further. Last edited by estost; 04-07-2022 at 08:22 AM.