Originally posted by Docrwm I thought I saw someone say that you can mount an adapter to a M42 mount lens semi-permanently and then it will work like a K mount. Is that not possible or a bad idea?
At the risk of re-starting the Adapter Wars, here's my take: 3 or 4 types of M42-PK adapters exist, with a great range of costs. These are:
1) The Official Pentax adapter, safe and boring and expensive. I say boring because it's best left in the camera, and you get to spend time (un)screwing lenses. I own one.
2) Cheap clones of (1), often badged as Bower. Cheap and exciting and YOU MUST REMOVE THE SCREW+CLIP OR YOU WILL GO APESH!T! Best left on the lens. I own dozens.
3) Cheap safe flanged no-infinity-focus adapters. Best for closeup and macro gear where you don't care about infinity, and some telephotos that focus past infinity. I own a dozen.
4) I have heard of (but not seen nor tried) an expensive adapter that safely allows aperture automation. I need to look into this further.
NOTE: I own many of types (2) and (3) because as well as being good serviceable adapters (and CHEAP, usually under US$5), they're also handy for modding some non-Pentax-compatible lenses. I only do minor surgery. But I digress.
The type (2) or Bower adapter arouses much controversy here. Unmodified, it is a pain and a disaster. Modified, I have had zero (0) problems with any. I put these on screwmount lenses, and generally leave them there. I use the rear lens cap as a wrench for tightening. I may put a piece of metal tape at the appropriate place under the adapter to enable Catch-In-Focus for that lens. Some of these have been in place so long that I've almost forgotten the lenses aren't K-mount.
The type (3) flanged adapter poses no problems. On a long lens, loss of infinity focus isn't severe. On a 200mm lens, far-focus drops to 100+ yards, no big deal if I'm shooting closer stuff. Some of these adapters are raw steel, some are painted black. I file away a bit of paint at the appropriate place to enable Catch-In-Focus.
* If you only have a few screwmount lenses and you don't intend to interchange their use with K-mount glass on the same day, the type (1) Official Pentax adapter is best.
* If you have MANY screwmount lenses and you wish to use some of them and some K-mounts on the same excursion, the type (2) is great. Ten of them at least.
* If you do any macro/close work with screwmounts, directly or with tubes and/or bellows, or if you have the odd lens that focuses past infinity, the type (3) is wonderful.
That's my story and I'm sticking with it.