Originally posted by Lowell Goudge I have not seen it mentioned yet here, but note that there is also another option.
Given that the optical design of all 50mm F1.4 lenses is essentually the same, since the 7 element super tak was introduced, it would be logical to assume that aside from either quality issues (sample to sample) or very minor design tweaks (element thickness and coatings) the performance of all 50/1.4 lenses should be the same, except for the early 8 element super tak, which is sharper.
Personally, I would go for the latest lens possible, because although SMC came out in the tackumar era, it did not stop evolving. therefore the coatings on an M lens should be superior to a SMC tak.
I beg to differ on the 'essentially the same' optical design of all the 50/1.4 (after it went to the 7 element Super Tak). While the changes are not tremendous, they most certainly are there between the S-Tak, SMC, Pentax-K, then the Pentax-M, and finally the Pentax-A (as you can see from Dimitrov's page)
While I never compared them against each other in a controlled test, from shooting all of these I certainly felt there was a difference to rendering (probably less of a difference in sharpness, where they are all excellent, than with microcontrast and bokeh). I found the first optical layout (that of the S-Tak, SMC Tak, and Pentax-K) gave the results most pleasing to me (having tried both the S-M-C Takumar and Pentax-K versions, by the way).