Just to repeat a discussion we already had for the 30mm/1.0 ...
For a f/1.0 with an optical construction where entrance and exit pupil have the same diameter (this is the case normally -- even for tele or retro-focus lenses with a protuding rear element), the diameter of the mount hole must be the registration distance which is 45.46 or 45.50 mm. But it only
is ~42mm. So, anything faster than f/1.1 should be extremely difficult to build.
Additionally, the PK mount was
designed to be just big enough to enable the 50/1.2 (which was said to be impossible with the M42 thread mount).
Theoretically, Pentax
could make a 50/1.0 and
accept vignetting right up to the center (effectively making it slower than 1.0). Could still gather more light than a proper f/1.2 when considering the entire surface. And with electronic correction of vignetting you get the f/1.0 shutter values ... So, it could be a marketing trick
[ Ah ... and no single pixel would see the entire exit pupil. Could make for an interesting bokeh fully open
]
I think this pretty much sums up all technical aspects of the issue. I am still thinking it is a hoax, though