Originally Posted by gpaual
also have the 50/1:1.2, and the 24 1:2.8 ...not sure if they are m or not, as it isn't stamped M so they may be f's
"F" lenses are auto-focus, basically a predecessor to the FA line. They should have "-F" after the word Pentax somewhere on the lens.
Lenses that are K-mount (as opposed to screwmount) and say "SMC" but don't have "-A" or "-M" after the word Pentax anywhere are generally referred to as "K" series, even though there is really no such official term. Then there are the non-SMC lenses; the ones generally available say "Takumar" and are referred to as such.