04-18-2015, 10:49 PM
An 85/1.2 is possible in the throat of F mount but not without lots of vignetting. The double-Gauss form has about 92% vignetting (100% -> 50% -> 25% -> 12.5% -> 6.25% illumination) or so with a rear element diameter of 40mm. That's about 4 stops. Size it up to 44mm and you're looking at more like 80% vignetting.
If it's a true 1.2 (which I doubt) it is enormously vignetted. If it's morel like f/1.25 or even f/1.28 then it will be vignetted less. I have actually seen real F numbers into the f/1.35 range for "f/1.2" lenses. At faster F numbers than f/2, the aperture spec is mostly a suggestion. E.g nikon 24/1.4 - f/1.45 instead of f/1.4. At slower apertures it tends to be pretty exact.
If it's a true 1.2 (which I doubt) it is enormously vignetted. If it's morel like f/1.25 or even f/1.28 then it will be vignetted less. I have actually seen real F numbers into the f/1.35 range for "f/1.2" lenses. At faster F numbers than f/2, the aperture spec is mostly a suggestion. E.g nikon 24/1.4 - f/1.45 instead of f/1.4. At slower apertures it tends to be pretty exact.