Originally posted by RKKS08
I am also asking because I read somewhere, that many Pentax 645 lenses are stellar performers also with APS-C, but the lenses of the Pentax 67 not at all.
Performance or ergonomics, two different things altogether. I have SMC Takumar 300/4.0 P67 lens that I shoot with a generic P67 to PK adapter on a K20D. The image is very sharp corner to corner because I am literally shooting through the centre of the lens. Ergonomically, it's not so good; the lens is larger diameter than most, long and heavy. There is no tripod mount on the lens and nothing available on eBay, the tripod mount on the generic adapter sit much too far back from the centre of balance to be of much use even on a tripod. I have made a palm rest for the lens with a tripod mount socket located closer to the centre of gravity for the lens and camera combination which better balances the setup on a tripod.
Same ergonomic problem also exist for CZJ Sonnar 300/4.0 because the lens is just as long and heavy as P67 SMC Takumar 300/4.0. The disaster hoanpham met with his Mir won't occur if the P6 lenses are used in normal shooting mode (no tilt adapter) because of the obvious size difference between the aperture ring and the P6 to PK adapter's breech lock ring, and the fact that they are far enough apart from each other would make confusing the two virtually impossible.