It looks almost exactly like my Retina Reflex IV lenses. The only difference is in the top left hand corner, the two scalloped indents just above the big notch are not present on mine. They did make a lot that looked like that, there were both Rodenstock and Schneider variants (not interchangeable so that the RF versions wouldn't get confused or something). There was also something very similar for a Bessamatic. All of the above can be called Deckel or DKL mount, they'll only work on the cameras for which they were made without interchanging, but all of them can be mounted on a regular SLR via Dead Link Removed to EF or M42, etc.