I recently picked up a barrel lens Xenar 180mm that I plan to put in shutter. Before I dismantle it though, curiosity got the better of me and now I'm wondering what behemoth of a camera uses a mount like this. It's made out of solid iron or steel. As you can see, it has a square end to the mount. Any idea what this lens has been attached to? The serial number dates it to about 1960.