This is quite confusing: Tomioka made a 55mm f1.2 lens under the Cosina name, the “Cosinon”, which was an M42 lens. This same lens was also sold as “Yashinon”, “Chinon”, “Revuenon” and “Tominon”. All of these Tomioka lenses are M42 mount. There is also a 55mm f1.2 Cosina lens with Pentax PK mount (possibly also made by Tomioka but different optically). In addition Porst also made a 55mm f1.2 lens for the Pentax PK.
Both of these PK mount lenses are very different from the M42 lens. I actually bought my Cosina 55mm f1.2 thinking it was the M42 mount. I was chagrined at my mistake, but it turned out to be fortuitous for me, since I prefer the bokeh of this lens. The M42 version has rather smooth bokeh, which many people like. I am much more a fan of this Cosina lens.
Have a look and see what you think.
