Originally posted by Ubuntu_user Oh, I didn't think that adapting PK lenses to the alpha mount was that bad... I just read not long ago about somebody here that adapted their A 50mm f/1.2 to Alpha mount and ran it on their A900 FF camera.
Going PK-->Alpha isn't a real problem. Going Alpha-->PK *is* a problem, and that's the OP's dilemma. The hangups are throat size, and register. Long-register lenses can (theoretically) be fitted to short-register cameras and retain infinity focus, but not the other way around.
Registers: Nikon= 46.5mm - Pentax= 45.46mm - Alpha= 44.5mm
It's no big deal for me to force-fit a Nikon lens to a Pentax mount; their bayonets are nearly identical, with lens throats of 44mm diameter. It focuses slightly past infinity. But a Pentax lens on a Nikon camera either won't focus to infinity, or needs an optical adapter that acts as a short TC and reduces IQ a bit. An Alpha lens on a Pentax camera has the same problem.
The Alpha bayonet is a different size, with lens throat of 49.7mm diameter, which is wider than the entire Pentax or Nikon bayonet. A Pentax or Nikon lens could have its base removed and replaced with with an Alpha base (and no AF, of course.) But not vice-versa. With MAJOR surgery, well maybe, but probably not. So even without the register disparity, the Alpha lens just won't squeeze down the Pentax throat.
Last edited by RioRico; 09-12-2011 at 04:27 PM.