Peter, I am trying to identify the mount of this lens. It locks like a bog-standard 50f1.5 - apart from the mount. Professional job too. the mount is held in place by four screws inserted from the lens side of the mount - which of course means that i am going to have to remove the helicoil to get to them. I had faint hope that they were tapped through the back of the mount.
The machined flange part looks like it was done by a pro - but a pro with a rather crappy cutting tool as the marks are clearly visible.
There seem to be no means of attaching it to a mount - unless it was held in by something from the front.
Both helicoil and aperture ring are fully functioning so that more or less excludes a X-ray lens as these are usually fixed focus and aperture.
Somebody suggested cine camera, which could be a possibility. Cradle mount and a clamp holding it in place in te machined part - but why then the infinity lock?
It has an E-P marking and the # 23166.
I will try to get it apart - at least to check if the 39mm thread is still there. The mount has some kind of shield for the back of the lens element pack.
Never seen a mount like this and it is rather intriguing , so any help would be appreciated.