The 645 AF 120/220 Film Back Insert permits fast changes of film. Change from 120 to 220, black-and-white to color, roll film to Polaroid or attach a digital back. The innovative design of the Mamiya 645AF 120/220 Film Back Insert allows for the use of 120 or 220 film simply by rotating the pressure plate. Film is held perfectly flat in both 120 and 220 modes. Incorporated into each magazine is an automatic film advance with automatic advancement to the first frame. Merely drop film into the back, press the shutter release button on the camera and the magazine automatically advances the film to the first frame. There is no need to align the "Start Mark." The LCD panel shows film speed, film type (120 or 220) and the number of exposures at the touch of a button. All of this information is transmitted to the camera body, AE Prism Finder and lens to assure correct exposures. It incorporates an internal backlight for viewing information in low light situations and the battery backup lets the photographer view information even when the magazine is not attached to the camera. All Mamiya 645AF film backs have built-in fail-safe features for easy operation. The dark slide is locked when the Roll Film Magazine is not attached to the camera to prevent accidental exposure; the shutter cannot be released with when a magazine is attached to the camera, unless the dark slide is withdrawn; the magazines cannot be removed from the camera unless the dark slide is insert; the shutter cannot be release without a battery inserted in the magazine.