Pentax M42 Adaptors, the good and the bad.

Lloydy · Expire: 2022-01-01

Pentax to M42 adapters, always a subject for some discussion, with the general concensus recommending the genuine Pentax adapter, and a few of us also recommending good quality adapters from independant manufacturers. I've been a champion of the British made adapters by SRB Griturn that I've always found to be reliable and excellent quality, and cheaper than the genuine ones.
But I think we all agree the cheap and nasty ones should be avoided

I have a genuine Pentax adapter, a few SRB adapters, and recently I found a cheap unknow brand adapter at the local camera fair. When I looked at it closely I could see that there was some brass showing through the plating, so I got a good adapter from my bag and compared them. I didn't like what I saw, but I paid for it because I wanted to see what was happening to make the wear on the adapter. It soon became apparent that the wear was due to the lens and adapter over rotating in the camera body mount!

Once I got it home I tried it with an old lens on a camera mount that I have removed from an old ME Super that I use for experimenting. When I fitted the lens and adapter to the camera mount the adaptor span one notch and came out, there was no dead stop for the adaptor.
And this is why.

The unknown adapter is machined differently in this one important place, there is a curve instead of a right angle at this point, and the curve allows the spring steel stop in the camera mount to ride up allowing the mount and lens to over rotate and come off. This curve is quite clear in the last picture.

The SRB and the Pentax adapters have a right anle that contacts the stop firmly and will not allow it to ride up. The second picture shows the SRB adapter which is identical to the genuine Pentax item.

In two of the pictures you can see the 'stop' that is part of the camera lens mount, it's a thin section of spring steel that butts up to the right angle on a decent adapter.

Both the SRB and the Pentax adapters are made so the stop in the mount works in the same manner as it does on Pentax lenses, all of mine have the right angle and not a curve.

My unkown one was going in the bin, every time I tried it on the lens mount, and it rode up over the stop, a tiny sliver of brass came off and could be seen with a loupe on the camera mount stop, and that's something I don't want in my camera. But I have saved it by making the curve into a right angle with a Dremel, and it now works perfectly.

Post edited with new pictures after Photobucket lost the originals.

Nesster · Expire: 2014-02-20

A bit of Dremel will do ya. I actually bought a Dremel to do some household stuff with the idea of taking it to one of these adapters. Haven't got around to it ye.

Your pics and explanations are exemplary; maybe you ought to post this over at pentaxforums.com as well Wink

Lloydy · Expire: 2022-01-01

Yes. I will almost certainly remove the curve and use it on one of my lesser used lenses. But that's the engineer in me, I can do that. A lot of people need to see the difference and be VERY wary of using an adaptor that has a curved shape on the 'stop'.

I have posted the same thing on the Pentax Forums, I think it's worth spreading the word as to why some of the cheap adapters are bad. Perhaps it's common knowledge ? But what the hell, it's worth repeating.

elliott · Joined: 16 May 2011 Posts: 170

Very informative post, I have one of the cheap unbranded adapters and it always annoyed me when it over rotated in the mount. I always thought the official one had some form of stop to keep that from happening.

Seeing that it was just a simple machining difference on the little tabs prompted me to break out the Dremel immediately. I squared off all of the little tabs and the adapter no longer over rotates. I even put it on my junk film body and tried to force it a little before putting it on my K100D, no problems at all.

I was close to buying an official Pentax adapter to solve this problem and I still might get one, but for now I am happy with my $7 unbranded adapter.

I am going to pick up one of the cheap flanged ones that don't allow infinity focus, it should work well on my Mamiya 60mm macro, the focus is so stiff that it keeps coming unmounted and I don't want to drill it for the lock. I did disassemble and lube the helicoid on it and it helped, but I think it is just naturally stiff.

Lloydy · Expire: 2022-01-01

I'm pleased it helped Elliot. It's possibly just cheaper to machine that way, although in these days of CNC machines there really is no excuse to make something with a basic design flaw. Especially when you have the original to copy.

I've Dremelled mine as well, and it works perfectly now.

Lloydy · Expire: 2022-01-01

The pictures are missing because Photobucket has lost a bunch of pictures ! Mad

I will restore the pictures as soon as possible, I'm away from home at the moment.

Attila · Expire: 2025-11-18

Use built in upload here to not get lost again.

Lloydy · Expire: 2022-01-01

Pictures restored at last. And the modified adapter is working perfectly after the modification.