The Mercury II’s odd half moon top was required to house the large rotary focal plane disk shutter that rotates at 1/10 sec. during the exposure. Times are varied by changing the slot opening in the shutter, an adaptation of the cine camera shutter design. The mechanism is extremely accurate and reliable and permits times as short as 1/1000 sec. It is a half frame camera and provides 72 exposures on a standard 36 exposure roll of film. The body of the camera is die cast aluminum and is decorated with Depth of Focus scales and a comprehensive exposure guide.