|Graflex 4x5 double dark slide|
image by Geoff Harrisson (Image rights)
A dark slide is a sliding cover, commonly a very thin sheet of metal, that closes part of a camera to light.
The term has come to mean a holder for a sheet of film (or previously a glass plate), in the form of a shallow box, closed by a dark slide (these holders are commonly double dark slides, containing two sheets of film, and with a dark slide cover on each face). Most large-format cameras accept film in this way. The dark slides are loaded in a darkroom or dark-bag, and the camera can then be loaded in the field in daylight. Once in the camera, the dark-slide cover can be withdrawn without exposing the film.