Question about M42 to PK adaptors

I have two of these adapters, one genuine Pentax and one one a copy. Both of them have a spring that locks into the mount on the camera so that you have to unscrew the lens and then remove the adapter. I've read in several places that removing this spring means you can leave the adapter permanently on the lens, which is what I would prefer to do. However, without the spring the adapters do not lock in place in the camera mount, and can rotate freely. This makes focusing impossible as the whole lens rotates. Does anyone know why this is, as the adapter looks identical to a PK mount on a lens? Is there a fix?

Mine are used similarly to yours, but I've further modified my adapters by drilling/filing a slight recess for the pin that locks PK lenses in place.
After making this recess, I use thread lock if the M42 thread is loose enough for the lens to turn.

Thanks, Mike, will try that, if I can work out where to drill.

Hi Jon, I am a bit puzzled as to why the whole lens rotates? If this is the case then the adaptors must be an extremely poor fit, as I do not have this problem with any of mine. I haven't bothered drilling at all because mine fit pretty tight; I have four of these and all are permanently attached to lenses and all fit exactly the same, all are secure.

I have made sure with mine that the adaptors are tightly screwed to the lens, with a paper gasket between adaptor and lens if required, and I've had no issues at all. I've removed the spring clip on all of mine.

Regards
David

I've tried them both on my two M42 lenses, David, and can't get them to work without the spring clip. Both of mine don't lock into the mount without the spring clip, and the non-Pentax one seems quite a loose fit, the lens wobbles around.

If we think back to when the K mount was introduced, many people would have large numbers of screw thread lenses. The Adapter K effectively converts a K body into a screw mount body to they could update the body and still use the lenses.

That's the way it works. You put the adapter on a lens and then fit the lens to the body. Then you can unscrew and replace that lens with any other screw mount lens as desired. This requires the clip so the whole lot doesn't fall out.

Some marques do it the other way round, where each lens has to be adapted. Obviously there are advantages to both approaches, but the Pentax way is simple and only needs one adapter per body.

I understand why people might want to remove the locking clip, but it makes for more difficult working and has potential dangers. It doesn't take long to remove the adapter even with the clip. Not the Pentax one anyway, which fits properly.

That makes sense, John, but I've only got two M42 lenses. I'd prefer to convert my lenses to K mount rather than convert my camera to M42.