Anyone know what mount this is?

>>2885109
Canon EF.
Couldn't have been easier.

>>2885110
Literally the most plebs mount out there (albeit there are some great glass out there)

>>2885110
>>2885112
Someone had put a Sigma 400mm APO up on ebay without knowing the mount. I was hoping against hope it was a K-Mount.

>>2885112
>plebs mount

All electronic.
Twists the correct/intuitive way.
Wide enough for f/1.2 glass.
No stupid protruding pieces from old mechanical tech.

>behold: the lens mount of the gods

>>2885210
>Wide enough for f/1.2 glass.
how to spot someone pretending to understand optics

>>2885210
>Twists the correct/intuitive way.
there is no correct way, it's just custom/habit. same for focus and zoom direction
>Wide enough for f/1.2 glass.
So are Pentax K and Nikon F. Both of them made F/1.2 lenses in the manual-focus days. They just haven't bothered to do so in the AF era.

also thanks to the fact that F and K aren't all-electronic and still have those protruding mechanical bits, you can still use those lenses, which is more than Canon can say about its FD glass.

>>2885210
You can make a f/1.2 lens with a mount the size of a needle head. You don't know how aperture size is measured.

>>2885225
>how aperture size is measured
In millimeters, by the diameter.

The f number is the ratio between the focal length and the aperture diameter. Without being able to get the aperture wide enough, good luck getting your f/1.2.

>>2885304
this is only true if the aperture stop is behind all of the lens elements. If it is not, elements behind the aperture stop can bend the light further, which allows them to fit it through a smaller hole.

>>2885215
He's kinda right though. It's very hard to compensate for a narrow mount.
The initial choice of a too narrow lens mount (Exakta) is one of the big reasons Tokyo Kogaku (Topcon) wasn't able to compete any more with Nikon and other brands in the professional market and in the end quit the industry altogether. Their 58/1.4 was very highly regarded, but huge compared to other fast 50s, and other fast lenses never got out of the prototype stage because they wouldn't be able to make them cost-effective.

So while it technically is possible making fast aperture lenses with a small lens mount throat diameter, a wide diameter gives more freedom for the lens designers, and is definitely a good idea (and part of well though-out design).

>>2885304
Does putting the aperture in front change how you compute the f number? I don't think it does.

>>2885115
That's how you get really good deals on camera equipment. I've lucked out a few times when someone mislabeled or didn't fully label lenses.

>>2885314
I'm not familiar with Topcon.

All their cameras I found looked like cheap shit.

Why didn't they just make a new mount?

>>2886697
Their Topcon RE Super / Super D are the exact opposite of cheap shit. Probably the smoothest, most luxurious feeling film advance of any SLR (if you care about that sort of thing), and ridiculously well built. A Zenit feels almost plasticky in comparison.
They were the first camera's with TTL metering (2 years before the Nikon Photomic, and in-body so it also worked with a waist-level viewfinder!) and an automatic diafragm (_8_ years before any other camera).

Their RE.Auto Topcor lens series is also of very, very high quality, and still collectible today. The best ones are without doubt Leica/Zeiss-tier.
I'm still hoping to find their 300/2.8 for a reasonable price someday.

The choice for a (modified) Exakta mount was made because of compatibility with their older lenses.
One reason for not changing the mount, and for Topcon's demise in the consumer camera market in general, was apparently that Tokyo Kogaku had become somewhat of an "elephant graveyard" for Toshiba, where they dumped their older management. This made the company completely inflexible, and while they were at one point 8 years ahead of the rest, they wasted their lead and kept on making (more or less) the same camera, until they were overshadowed by the other manufacturers.

In their last years they made (or even just rebranded) cheaper cameras, probably those are the ones you saw. Don't get those, they're mediocre at best.