Originally posted by jhickson I bought a cheap glassless K mount to Canon EF mount adapter to mount this lens on my Metabones speedbooster, but the aperture pin (what sticks out next to the bayonet mount for Pentax SLR cameras to control the aperture) scrapes against the inside of my Metabones mount. It doesn't press against the glass itself, but rather a layer of felt that surrounds the glass on the inside of the speedbooster. I later discovered online that you cannot mount this lens inside full frame mounts because of this aperture pin that sticks out.
K-mount lenses don't have an aperture pin. There is an actuation lever, however ("I" in the image below).
Is that what is causing your problem? If so, your options are to saw the lever off (ruins resale value) or not pair the lens with the speedbooster.
As noted above, you might have better luck adapting M42 lenses, but even then, the actuator pin with that mount may be a problem.
BTW...here is my push back regarding the amputation option...
Steve