[Big Dave]

Steve,
The best solution is to remove the steel spring and mount the adapter permenantly on your favorite M42 lens. This way you have ease of use and don't wast a useful item. I have both types. Fixed and the Pentax pop in unit. I use the fix adapter most. I cut down the cheap flange type adapters, so that they work at infinity and leave them on the M42 lenses. You can even drill a detent hole in the mount with this method on the cheap lenses.

Dave

After this close call, I would quickly, without hesitation, throw the ***** thing away. (The adapter, not the camera...)

Steve

[Brianog]

The people who sell 3rd party adaptors are criminals. It is unknown the vast amount of expensive camera equipment that has been destroyed because of them.

[newarts]

I really hate to say this countzero but the real Pentax model fits perfectly, stops in the right place and at least mine comes off without any tools.
It's one place where I think that your foolish to use anyone elses product.

Although I suppose that it might be hard to get where you live.

I've looked pretty closely at Pentax and some third party adapters; they are very similar in dimensions.

The detail that seems to prevent the Pentax Adapter from over-rotating is that the fillets are sharp where the adapter's ears meet the adapter barrel. The left side of the photo is a Pentax adapter & the right side is a third party adapter.


The ear roots that seem to be most important are those flanking the spring location. I filed these fillets so they were square on my third party adapters which solved the over-rotation problem.

Probably the best thing to do is to notch the lens base so the locking pin will engage as the lens is mounted. this will positively lock the lens where it is supposed to be and will prevent the lens from falling off the camera during use and preventing it from over-rotating when mounted.

Carefully mount the lens with adapter, mark where a notch should be placed in the lens base, remove the lens adapter and make a notch in the lens base with a small file.

Dave

PS My Pentax adapter seems to fit no better than my third party adapters; a little sloppier fit than some in fact. In my experience, once you've over-rotated an adapter (which can be done with a pentax adapter as well as with third party adapters) and learned to recover, you won't do it again.

Another trick that can help is to bend the trailing edge of the adapter's ears so they rub against the mounting ring's receiving flange during mounting.