>>4166993>but with SLRs only canon EF can adapt pentax lenses and only with a dumb adapterCanon EF-S, not regular EF unless you're talking mirrorless EF (BMPCC6K and similar ones).
It blocks the mirror on Canon EF (full frame) cameras. Maybe it can be used in mirror lockup mode but sounds risky, imagine running out of battery or the camera leaving live view for whatever reason and the mirror hitting the thing. EF mount is the best to adapt stuff to but Pentax K is the exception. You can adapt M42 just fine though, which I'd expect a Pentax K shooter to have plenty of. After all Pentax K was made to be compatible with M42 lenses. Pic related, the official adapter.
