Originally posted by winglik There are 2 types of aftermarket M42 adapters, the one you bought will give you issue at infinite focus. The other type looks the same as the OEM pentax adapter, it seats flat with the mount, i am using it, no issue at all. Different between OEM and aftermarket is that OEM doesn't require any tool to attach or remove it. Aftermarket comes with a little tool for you to remove it or tighten it. so it's really up to you. of course most people will go for the OEM. you can search "M42 adapter" in the forum, there were alot of discussion it already.
Ah no, the adapter I have is the same as the OEM one, but uses the tool - which I don't have an issue with. What I didn't expect was that it would poke out from the mount by ~0.5mm.
I'll spring for a genuine one and modify this one as a spare.