Bought this lens adapter a few weeks back.
Amazon.com: Zykkor M42 Screw Lens to Pentax K PK Mount Body Adapter: Camera & Photo
Seems to work without any issues. I mainly purchased the lens because it was cheap and I didn't want to make too big of an investment if I didn't like using the m42 lenses. Now that I've got a little bit of experience with the m42 line, I've decided I'm going to stick with the ones I already have. Not as hard as I thought it would have been (still need a lot more practice).
My question is, has anyone ever owned this lens adapter and the original Pentax adapter? I'm looking into buying the original Pentax adapter but want to make sure it would be worth the investment. The Zykkor is only 10 bucks, so if it's going to give me the same results, I would rather pick up another Zykkor to have as back up.
I don't think the Zykkor gives any infinity focus issues, but I don't really know because I don't do any landscape shooting. To be honest, I've never even tried to get infinity focus, so I don't know what settings I would have to use in order to achieve it.
If any wants any details on the adapter, let me know and I will share my experiences with the adapter.