Originally posted by Just1MoreDave When you are considering which lens to buy, try to start by defining your needs as clearly as possible. . .
OK - 70's English Language & Literature BA here (degraded by time and usage):
To answer the question which is better (a comparative), one must first define good (as suggests Just 1More Dave above). That is, one must establish a standard against which all candidates are judged. I assert there are numerous standards against which the quality of photographic lenses are judged, especially in Pentax lenses. So . . .
Standard -> Comparative -> Superlative = Good -> Better -> Best
Are we comparing lens resolution? Go you
Yoshihiko Takinami's website to review the seminal Pentax lens tests, even if it is already 8 years old. Although Yoshi did not test the complete line of Pentax lenses there are tests of Super-Tak's through FA to FA Limiteds there. Sometimes legacy lenses have the best resolution, sometimes an FA or FA Limited.
Are we comparing construction quality? First define quality. I ENJOY the feel of precision-machined, hand-assembled metal lenses and I have large hands, so for me late Takumar and SMCP lenses offer a
better experience. M lenses are probably the smoothest operating non-Limited lenses - they probably represent the pinnacle of analog industrial manufacturing quality - but they are generally smaller than I find comfortable (heresy, I know, but this is all subjective).
Does that make legacy lenses BETTER than modern FA carbonite housing lenses? As a user, if your shots require absolute critical focus in variable temperature environments, probably not - engineering plastic is less susceptible to housing expansion/contraction due to temperature variation.
You can continue this process yourself. What I believe is apparent across the entire Pentax line and history GENERALLY is an expectation that lens optical design is superior to most other brands most of the time at a price point, and the best Pentax lenses are at least the equal optically of the best lenses ever, usually at a better price than their best competitors.