First version of this lens, it was produced from 1967 to 1972.
As the 18mm f/11 it is M42 screw mount, but gets complete optical redesign, full frame 180° on diagonal normal focusing and larger aperture, and a filter selector where you would look for the filter ring.
Also known as Super-Takumar.
Built-in filters: UV, Y2, O2.
Holder for rear-mounted gelatin filters.
Product Code: 43841
The slip-on cap is the 58mm one, the same one you can find on the first version of 28mm 3.5 M42 and on other Pentax lenses of the same age.