Fisheye question

Not the usual, but have a look at this diagram, part of a patent Canon has applied for. I assume the vertical line at the right hand side is the film/sensor plane? If it is, how on earth can the mirror flip up and down? There just isn't space for it to do so. In fact theres insufficient room for a mirror full stop.

If it's not the plane of focus, what else could it be?

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I'd buy a 15-24 fisheye.

No obvious sensor plane indicated, I assume that the line is the lens mount position.

Paul,

Why didn't that dawn on me. You sir are a great lateral thinker.

Weirdly, Canon have another patent with a completely flat front element looking very like a thick filter covering the next element which is normal.

Most likely it's the mount

Lowner wrote in post #9370598
Paul,

Why didn't that dawn on me. You sir are a great lateral thinker.

Weirdly, Canon have another patent with a completely flat front element looking very like a thick filter covering the next element which is normal.

What focal length is the lens?
Could be that it's a different refraction element used as a modifier for abberations, or as a protection - think front element of the L telephotos.

Here it is

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Why won't they just make a new 15mm prime 2.8 or 1.4 with USM
I might buy it