Speaking of Pentax lenses...

[lxdude]

Thank you lxdude for your explanations. I want to add that there were two M 42 lenses which had the name "SMC Takumar", these were the 1:1,8/55 mm and the 1:1,4 50 mm. They came with the Spotmatic F and the Asahi Pentax ES and ES II. These lenses were the only Takumars with a rubber coated focussing ring, all others were full metal. The optical construction was the same as the precursor types. Due to the change to the K-bayonet the rest of the M 42 lenses did not get the rubber coating.

Thank you for that information. I was not aware of that!

EDIT: I just went to look on the KEH site and see that there were 50mm/4 lenses with the rubber ring and "SMC Takumar" and 50mm/4 lenses with the metal ring marked "Super-Multi-Coated Takumar". Photo archaeology is such fun!