Originally posted by timw4mail There were a few 1.2 M42 lenses, too. I'm sure the M42 mount doesn't get all the benefit of a 1.2 lens either.

The M42 mount hass approximetly the same limit. You can calculate the actual value as (flange focal distance)/(rear element diameter) if you substitutes the sin in the equation by (half rear element diameter)/(flange focal distance).

The M42 mount has a diameter of 42mm, so I can imagine a 38mm rear lens element plus the 2mm screw all around to mount the lens. The FFD is 45.46mm and it gives 45.46/38=1.1963, so F1.2 as limit. The bayonet requires more metal around the rear elemnt to work, so the limit is approximetly the same.

Nikon F mount gives the same F1.2, Canon EF gives F1.0. M43 has a limit at F0.65 if I calculate correctly. There is a hard limit at F0.5, any lens faster then F0.5, nothing can be made that fast with air gap between the lens and the sensor.

---------- Post added 05-29-18 at 10:44 PM ----------

Originally posted by bavd So essentially you are buying a very expensive pentax A 50mm 1.2 ?

I think yes. And my educated gess about the bokeh is the same, it's limited to F1.2 I think. (but I'am not 100% sure)