Originally posted by Cerebum I thought that was the SX, my understanding is that the DX is fine. The auto Yashinon 55mm protrudes but I didn't try it. Maybe I should
The SX, meaning the Mayima? From what I remember, the Yashinon-DX 50/1.7 is the absolute worst lens ever as far as hitting mirrors -- even the DX/1.4 I think is ok (don't quote me on that). And probably the others you mention unless you've found out differently. (And I've got copies of all of those, don't think I've had that particular trouble with any of them.) There are are couple of others known for hitting mirrors on full-frame that I can't recall right now, but I don't think they were all in the same family or even necessarily adaptable to Pentax (Canon lenses, etc). As far as APS-C, the Yash DX/1.7 is the only one that comes to mind.
BTW, the later Yash DS-M 1.4 & 1.7 50s are totally fine in that regard and even better optically, although not as cool-looking...