A film holder is a device that holds one or more pieces of photographic film, for insertion into a camera or optical scanning device such as a dedicated film scanner or a flatbed scanner with film scanning capabilities. The widest use of the term refers to a device that holds sheet film for use in large format cameras, but it can also refer to various interchangeable devices in medium format or even 135 film camera systems.
The most common instance of film holder is the sheet film holder. Also referred to as a dark slide or double dark slide, they are flat devices, slightly larger than the films they hold, which commonly hold one sheet of film on each side. The plate holder, which is a very similar device, holds glass plates instead of sheet film. A dark slide, from which the device derives its alternate name, is simply a dark cover that slides into a recess in the holder to protect the film (or plate) from exposure to light. Many dark slides have differently colored bands or handles on each side, one usually light and the other dark, so the photographer can distinguish between exposed and unexposed film.
Traditionally, sheet film and glass plate holders have been made out of wood. Wooden holders, properly treated, can last a very long time, and apart from possible warpage, many very old specimens are still in service. Some companies continue to make wood models today, particularly for more uncommon film sizes, and as many are mostly handmade, they can be quite expensive. The majority of new sheet film holders are now made out of plastic.
When using a sheet film holder, the device is inserted into the camera, often a view camera, and the dark slide is withdrawn, making the film available for exposure. After the exposure has been made, the dark slide is reinserted into the film holder, and the device is removed from the camera for later processing of the exposed film.
Some film holders can hold more than two sheets. One of the most common is the Grafmatic, manufactured by Graflex, which holds six sheets of film in individual septums. They were available in "23" and "45" models, corresponding to 6×9 cm (2¼×3¼ inches) and 4×5 inch sheets. It takes little effort to quickly cycle through all six sheets, which makes the Grafmatic ideal for press camera usage. Burke & James produced a similar device called the Kinematic, which holds 10 sheets, though was only available in 4×5 inch format.