Originally posted by jatrax Only speaking of the OEM one, very simple. Just insert it into the camera and turn to lock, just like a lens. Then thread the lens onto the camera. To take off, just reverse the process.
...or thread on to the lens or tube and mount the combination to the body as with a native K-mount lens. Both methods work and both can be found in the various Pentax user guides out there. I find it easier to spin the adapter onto the lens, particular with the larger telephoto lenses.
In regards to the types of adapters. As noted above, the flanged adapters are dirt cheap and work well for use with extension tubes and bellows. They do not work well if you need infinity focus.
It is with the non-flanged adapters that things get sticky. Those always allow infinity focus, but the non-Pentax (brand-X) adapters can be problematic. The most common issue is the adapter becoming stuck on the camera.* The work-around is to remove the small retention spring. This allows for easy removal, but also allows the adapter to rotate freely in the mount (not locked on the camera). Some users have drilled or notched the base of their lens to engage the K-mount lock pin as an additional work-around. There are also reported issues with over-rotation in the mount, poor materials, and (in a recent thread) inadequate seating onto the lens threads.
So, what about the official Pentax unit? They always work. The rub is that they are often expensive and even more often, very difficult to obtain. Other options might include the SRB Griturn adapter from Britain. At last report they were made by SRB in Britain, have an excellent reputation and are not too expensive.
Pentax M42 adaptor|M42 lens| Pentax K
Good luck and enjoy exploring the world of M42 glass. It is truly worth the effort.
Steve
* I learned the hard way in regards to brand-X (in this case Bower) adapters. It took me almost three hours of fiddling to get it off my camera. I actually had the Dremel tool handy to cut it out of the body, but fortunately did not have to take that drastic action.