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 films. A dark slide, from which the device derives its alternate name, is simply a dark cover which slides into a recess in the holder, to protect each sheet of film (or plate) from fogging or unwanted exposure to light. Many dark slides have differently colored bands or handles on each side, one usually light and the other dark, to allow the photographer to distinguish between film which has been exposed and that which hasn't.
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When using a sheet film holder, the device is inserted into the camera, often a view camera, and the dark slide is withdrawn, making the film available for exposure.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.
There are some film holders which can hold more than two sheets. One of the most common is the Grafmatic, manufactured by Graflex, which holds 6 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.
Graflex also produced the Film Magazine. It is commonly referred to as a "bag magazine" (or "bag mag"), and uses a leather bag which hangs on the side of the frame to exchange the septums from front to back. It is a much more manual device than the Grafmatic, as exchanging a septum is done manually through the bag, rather than by a simple manipulation of the magazine's dark slide. They were sold in separate versions for film and glass plates, and held 12-18 sheets/plates, depending on the model. They are found in 4×5 and 5×7 inch formats.
Though all are superficially similar (a "bag mag" film (not plate) septum is the same thickness as a Grafmatic septum, but has slightly different width and length; a Kinematic septum appears almost identical to a Grafmatic septum but is in fact considerably thinner) in fact use of a septum from a different type of holder in any of these multi-sheet holders is very likely to jam the entire magazine and bend internal parts, which can then damage yet another holder if used with it. As replacement parts are no longer available one must be careful not to interchange pieces of different types of multi-sheet holders.
Fuji created a 4x5 system in the late 1990s called QuickChange, which is somewhat similar to a Grafmatic in principle. It is made of plastic rather than metal, making it lighter, and less prone to bent septums, but also less durable. It can hold 8 shots, and inserts are purchased already loaded with film. Though not sold as such, these inserts can be reloaded a limited number of times with standard sheet film. Because the Fuji holders used sheet film of normal thickness, they offered higher image quality, but never became widely popular before digital imaging brought much production of traditional large-format materials to a halt.
Graflex and Polaroid produced film pack holders which could be loaded in subdued light. Film packs were available from various film manufacturers in 12- and 16-sheet units; the classic film pack consisted of several "sheets" of film (actually much thinner than standard sheet film as these were cut from large-format roll film, for economy and for physical flexibility) taped together and wound in a series of S-bends around a metal frame. To "advance" the film, the user pulled a paper tab which protruded from the side of the film pack and which was attached, facing the opposite direction, to the junction of each sheet and its intervening section of tape. Because of the thin film and only slight tension provided by this system, film flatness was poor and the resulting negatives were often sharp enough only for contact printing; thus they were primarily used by press photographers, and demand fell off dramatically as photojournalists converted to roll film cameras.
According to former Kodak employees at the Eastman House photographic museum, Kodak ceased production of film packs when the last employee trained to assemble them (which required working with the very sharp metal frame in total darkness) retired in the 1980s, thus rendering all traditional film pack holders in the world obsolete at once. Polaroid film packs, though somewhat mechanically similar, are not (and never were) available in standard film sizes. The Fuji QuickChange system was sometimes referred to as a film pack system, but as noted above was a mechanical multi-sheet holder.
Until 2008, Polaroid was the producer of the widest range of instant sheet and pack film. Their exit from the market leaves only Fujifilm as an instant film producer. The Polaroid 545, the lighter and more modern 545i, and the 545 Pro backs are 4×5 inch instant sheet film holder used by many photographers. Polaroid also produced 8×10 inch film holders and films. Polaroid and Fujifilm both produced 10-sheet 4×5 inch instant film packs and holders.
Some 4×5 inch films are supplied in light-tight envelopes which can be loaded into a special holder in daylight. The envelopes are much smaller and lighter than a dark-slide loaded with film, allowing a larger quantity of film to be carried than the same amount of film in dark-slides. Fuji Quickload film and holders, and Kodak Readyload film and holders, are of this type. A useful discussion on the merits of the various systems, and other information on cut-film holders, is to be found here
Film holders that allow rollfilm to be used on cameras normally used with sheet film are usually called film backs. Film backs for 4×5 inch cameras are particularly common—there is little point in taking 6×9 cm pictures on a 20×25 cm (8×10 inch) camera. Horseman, Linhof, Graflex, and other manufacturers have made roll film holders in 6×7, 6×8, 6×9, 6×12, and 6×17 cm formats. Some models can slip under the ground glass like a normal sheet film holder, while others require the ground glass to be replaced by the roll holder.
Film holders are available as accessories for some medium format cameras. The most usual case is the Polaroid back taking instant film, often used to check exposure values, color rendition, etc. before taking final photographs on conventional film.
Several of the types of holders made for large format film, including darkslide sheet holders, Grafmatic multi-sheet holders, the Graflex bag mag, and film packs were also manufactured in medium format sizes, almost always 2 1/4"×3 1/4" (6×9cm). Press camera manufacturers often produced smaller versions of their 4×5 cameras in this size, often called "23", and while later versions of these cameras could use rollfilm adaptors, these were not widely available until almost 1950, and were expensive in the their first years of production.
Sheet film or glass plate holders for medium format rollfilm cameras can be found, but are of mainly historical interest. Some rollfilm cameras have interchangeable backs to allow films of different types to be used. Some 35mm cameras have motorised backs which may hold longer than normal lengths of film, with a mechanism which automatically advances the film after each exposure.