Just realized this can't possibly be a Nikon mount, since the F-mount is limited to f/1.2. If the lens does cover 24x36mm I assume its something like a Sony E mount.

The limiting f/# for a lens in air meeting the Abbe sine condition (i.e., corrected for spherical aberration and coma) is f/0.5. At this point the marginal rays are perpendicular to the optical axis, or parallel to the image plane, so its a pretty obvious limit in some ways.

f/0.55 (i.e., NA = 0.91) is not completely unheard of. There are some extremely high-power microscope objectives designed to work in air (i.e., not oil immersion) that approach that value.

Regarding Speed Boosters, the 0.58x BMPCC Speed Booster is designed to produce f/0.74 when used with an f/1.2 lens (more accurately f/1.2599). The limit of f/0.74 is set by the clear aperture of the first few lens elements in the Speed Booster. If you attached a lens faster than f/1.2599 you would still only get f/0.74 out of the lens + Speed Booster system.

As far as I am aware, f/0.74 via the 0.58x BMPCC SB is the fastest lens you can buy today. There are a handful of lenses in the history of photographic optics that have been faster than that, the Zeiss 50mm f/0.7 being the most famous example.

Incredible! I'm excited to hear more about this lens.

Because it is absolutely unheard of.

Obviously I wasn't wrong about the condescension though.

My confusion is largely due to the fact that very recently Brian Caldwell stated that an f1.2 lens with the 0.58x Speedbooster is the fastest lens in the world. When I saw this Mitakon lens was Nikon mount, I thought perhaps that statement was no longer true.

Ok... interesting math, but posting that link as an 'explanation' was interpreted by me as a bit condescending, as I know what an F stop is and you should probably have noticed by now that I'm not an idiot who just asks dumb ass questions on the forum.

Either you did not understand my question, or I am not understanding your 'answer'.

I'm talking about what happens when focal reducing by 0.58x a lens that is f0.95.

The math says light transmission of a 0.58x focal reduced f0.95 should equal roughly f0.55 (using the f stop scale as reference), but that just sounds insane and impossible, which is why I wanted to find an answer.

Wait, what happens when you use this with the BMPCC speedbooster? f0.55 can't be possible... right?