Abstract: In a magnetic disk cartridge, a dial member is rotatable relative to the cartridge housing to a plurality of positions for indicating the number of tracks recorded on a disk surface. A resilient locking finger is connected to the dial member for engaging respective engagable means on the housing, which correspond to the various track number positions. Whenever the cartridge is removed from a recording and/or playback apparatus, the locking finger engages one of the engagable means to prevent the dial member from rotating out of the last position to which it was rotated. An access opening is provided in the housing to receive a rotational driver of the apparatus for rotating the dial member to its track number positions. The locking finger is supported for movement by the rotational driver to separate from any one of the engagable means as the driver is received through the access opening, thereby freeing the dial member for rotation by the driver.

Abstract: The back of a camera has a window through which an information area on a film cartridge may be viewed. One of the ends of an elastic opaque strip is connected to the camera back at a location between the window and a film pressure plate supported on the camera back. When the other end of the strip is moved to draw the strip taut, partially about the cartridge, the strip transversely shifts against the cartridge and positions an opening in the strip, aligned with the window, over the information area on the cartridge. The strip thus forms a light-tight connection between the camera back and the cartridge, which prevents light entering the window from fogging film advanced out of the cartridge.

Abstract: In a bottom-loaded camera, a light seal is located between a loading chamber adapted to receive a film cassette and a window in the camera back for viewing film-related information on the loaded cassette. The light seal is movably connected to the camera back in light-sealing engagement therewith and shields film from the cassette against light entering the window. Manual operation of an exterior member, moves the light seal away from the chamber to provide space for loading the cassette in the chamber, and against the cassette to effect a lighttight connection between the camera back and the cassette.