Reflex Korelle

This camera was made by Franz Kochman, Dresden, Germany.  The model was launched in 1934, but I'm not sure which version I have, so it may be a year or two later.  It's a single lens reflex taking 6 x 6 cm shots on 120 film (like a Hasselblad).  It has a waist level viewfinder, with a magnifier, like a typical twin-lens reflex, but it also has a mirror that is raised when the shutter is pressed, and a focal plane shutter.  The lens is a Schneider-Kreuznach 7.5 cm f/3.5; it's supposed to be interchangeable, but I can't get it to move so far. The shutter has speeds from 1/500 to 1/20 and B.