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08-28-2013, 05:24 AM   #1
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Solution to Genuine Pentax M42 Adapter problem!

Just thought I'd relate an experience of mine here in case anyone else has had the same problem with a genuine Pentax m42 adapter.

My adapter was one of two adapters that came in a lot of lenses with I bought 7 years ago, so it was most certainly not new. I have used it off and on with the spring intact for that period. The second adapter didn't have the spring, and I've always felt more comfortable with the adapter locked onto the body after mounting the lens.

Recently when un-mounting a lens I felt a curious shift when unscrewing it from the adapter. After completely removing the lens I came to discover the adapter had rotated during the un-mounting process and was rather jammed. Careful manipulation allowed me to remove the adapter without damage to the lens mount, and I discovered after removal that the retaining spring and screw had come off, jamming the adapter in the mount. Luckily I found both and the screw didn't fall into some horrible part of the mirror/sensor chamber where it was stuck!

I tried to re-install the spring and screw, and tested without a lens - the screw popped right back out once the spring was slightly compressed- obviously the screw was stripped out! I know I can use the adapter without the spring, but one of my flea market finds was a SMC Takumar 200mm f/4. Heavy sucker, and it does start to work loose in use without the adapter locked onto the body. I still need an adapter that can lock in place!

Of course now that Pentax has stopped manufacturing the adapter, they command premium prices on eBay and elsewhere. I ordered a cheap Chinese made adapter to try- a complete disaster. Thankfully I tested it with a very inexpensive lens. Threads are so poorly machined that they started shearing the lens threads (I didn't force it once I felt the resistance!) so I stopped immediately.

What do to? I started thinking, if I had a micro tap and die set, I could install a slightly larger screw on the genuine Pentax adapter. But I don't want to spend 50 bucks on the equipment!

Solution- I took the adapter ring with the spring to a local jewelry shop that repairs watches as well. I explained the problem, and the repair technician (who also knows a bit of photography, that helped!) said it was completely repairable.

I picked it up yesterday- works like a charm! his work was expert, the screw doesn't protrude into the threads, he did what he said was a "reverse thread" on the tap into the adapter ring body so the screw is held incredibly tight, he even put a touch of lock-tite in place (not that he needed to with the reverse thread tap).

End cost of the repair? $10.00. Much better than a minimum of 45-50 dollars trying to buy a replacement off eBay! Of course I threw away the Chinese adapter which was a $7.00 waste, but I kept the screw and spring in case I ever decide to put the second adapter I own back into service so it can lock on the body!

08-28-2013, 06:01 AM   #2
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For future adapters... you might want to consider using some type of lock-tight solution.
08-28-2013, 06:55 AM   #3
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QuoteOriginally posted by mrNewt Quote
For future adapters... you might want to consider using some type of lock-tight solution.
Given the size of the screw and where it mounts, I can't see lock-tite being that efficient at preventing the same sort of thing happening again. The threads in the adapter body were stripped out, and this was just from using the thing.

Just to say that the whole design is slightly flawed in the fact that the screw that holds the spring in place is so very small and fine that it will eventually strip out just due to the force of the spring being compressed and released as the adapter is mounted. Actually two screws on the spring would have been a more viable solution, spreading the force on the spring across two mounting points instead of just one.

I have a feeling it was a cobbled together solution on Pentaxes part to begin with- they needed to do something in the late 70's to address the need of all the owners of Pentax m42 glass that were probably a bit miffed at the shift to a bayonet mount. It's not like there was an obvious solution in the design of the bayonet mount to lock an adapter in place. They realllly should have considered modifying the registration distance of the K mount so that an adapter for m42 would extend slightly from the K mount.

Basically the adapter I had repaired failed due to it's age and the design flaw. I wanted to get it back in working order in such a way that I knew the inherent problem was dealt with. I worked on an electronics repair bench for 7 years, and that was always the rub when repairing mechanical systems- fixing for the long term, not just to "get it working" again.
08-28-2013, 07:09 AM   #4
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If there is even the smallest play / gap, the treads will get stripped out in time while you are applying constant "pressure" on them.
By using lock-tight you create a stronger bound between the screw and the the place its screws in, reducing the gaps between threads making a "stronger unified thread".

08-28-2013, 07:26 AM   #5
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A drop of red lock tite will make it where it can never be disassembled again, whcih in this case should be a good thing.

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