What Lens mount is this? (It's an old lens)

TexPhoto

EOS R
Apr 15, 2011
1,240
35
San Juan, PR
Can anyone tell me what lens mount this is? There are no threads, just a smooth ring. And while it looks like it should come off, so far it has not.

I want to mount an EOS mount so I can use the lens. It's an 1100mm MTO f10.5 Russian Lens btw.

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