It's pretty easy (though a bit of a shame) to modify the lens so that it clears the mirror. One has to file down the protective rear housing (very carefully).
Originally Posted by Tony-S
+1 for Super Tak 50/1.4
+1 for Super Tak 28/3.5 (a stupid stupid sharp, fun lens)
+1 for Super Tak 105/2.8, though I just sold mine because I never use teles
+1 for Super Tak 35/3.5, though I have only used the optically similar K version
+1 for using these lenses on a spottie instead of an EOS film system. I have done both, and Spotmatics provide a more rewarding experience.
Better yet, get a camera with a better viewfinder like a KX or MX and get an M42 adapter to leave permanently on the camera. Big viewfinders = big fun!