Peter J. Alling wrote: "If I remember correctly Cosina's K mount 1.2 normal lens was a 58mm. They are apparently hard to find and rather expensive thought."
Cosina's K-mount f/1.2 normal lens was 55mm, like all other third-party f/1/2 lenses in K mount (Porst, Rikenon, Revuenon, Vivitar) or screwmount (Fujinon, Tomioka, Vivitar, Yashinon). The Cosinon's filter size was 58mm. Konica made a 57/1.2. Minolta may have made a 58/1.2. Someone made a 60mm in th e1960s or 1970s, because I own several old books on how to take better pictures, and I kept seeing the 60mm pop up in the credits. Paul Stregevsky
