Sejanus.Aelianus
Veteran
I once owned a Rikenon f1.2 with a Pentax screw mount. It was notable for having a sector of the rear element cut away to avoid fouling the aperture activation pin. I found that it was OK at full aperture, for which read "better than nothing in available dark", but pretty poor once you stopped down past f8.
That cured me of using anything past f1.4.
That cured me of using anything past f1.4.