Hi, I recently got a Schneider-Kreuznach Xenar f2.8 38mm lens which I thought was a D mount but it turned out the rear diameter was a little bit bigger then a D mount. It is about 17.5mm on the thread. The thread is intermitent and there is writing on the two areas where there is no thread. One side says 12.5mm and the other side says M18x1. Does anyone have any idea what type of camera this size lens fits on. Thank you.