Originally Posted by Doug
Interesting, Colton.... I have a 28mm f/2 SMCP-M but it looks somewhat different. Same "grenade" pattern focus ring but looks shorter. And your front element looks more recessed than mine tho hard to tell. I got mine new in Nov 1981, noting this version was made 1980-84. It's 63mm dia x 42mm long, weighs 215g, has 8 elements in 7 groups, stops to 22, 6 aperture blades. 49mm filter thread. Uses clip-on hood PH-S49. Does your lens seem to be the same as this? Of course mine is an M version, may account for a difference...
Originally Posted by zuikologist
From memory the SMC-K version is a different beast to the SMC-M version. The K version is the Zeiss/Distagon Pentax.
BTW love your brassed KM Colton.
Zuigologist is correct, the very first Pentax K 28/2 came out of a cooperation between Zeiss and Pentax. Originally designed by Zeiss for cinematography, Zeiss used the design for the C/Y mount Distagon 28/2, and allowed Pentax to use it to build this lens.
The Pentax-M version is a different and original Pentax design.