 Nevertheless, Rollei's designer Ernst Moeckl revised the housing, and by changing the edge radius made the camera body even smaller.For the mercury battery PX 13 (= PX 625 = MR 9) of the light meter, a place was found inside the camera housing.The film rewind knob of the engineering model was exchanged for a rewind crank, and a hot shoe was added for mounting an electronic flash at the base plate.