Editing 135 film (section)

=== Cassette ===
[[file:Kodak-Max-400-35mm-Film.jpg|upright|thumb|A roll of [[Kodak]] 135 film for cameras]]

Individual rolls of 135 film are enclosed in single-spool, light-tight, metal cassettes to allow cameras to be loaded in daylight. The film is clipped or taped to a spool and exits via a slot lined with [[Flocking (texture)|flocking]]. The end of the film is cut on one side to form a leader. It has the same dimensions and perforation pitch as [[35 mm movie film|35&nbsp;mm movie print film]] (also called "long pitch", [[Film perforations#KS|KS-1870]], whereas 35&nbsp;mm professional motion picture camera films are always "short pitch", [[Film perforations#BH|BH-1866]]).

Most cameras require the film to be rewound before the camera is opened. Some motorized cameras unwind the film fully upon loading and then expose the images in reverse order, returning the film to the cassette; this protects all exposed frames (except the last one or two), should the camera back be accidentally opened; unexposed film gets spoiled, however. [[Disposable camera]]s use the same technique so that the user does not have to rewind.

[[File:DX-Codierung asb PICT3739.JPG|thumb|right|This modern film canister uses [[DX encoding]]; it is marked with a six-digit barcode which embeds the [[DX number]] below a silver-and-black conductive DX Camera Auto Sensing pattern.]]
Since 1983, most film cassettes have been marked with a [[DX encoding]] six-digit [[barcode]] pattern, which uses a [[DX number]] to identify the manufacturer and film type (and thus processing method), and the number of exposures, for the use of photofinishing laboratories. The cassettes are also manufactured with a Camera Auto Sensing code constructed as two rows of six rectangular areas on the metal cassette surface which are either conductive or insulating, representing 32 possible film speeds, eight possible film lengths, and four possible values of exposure tolerance or latitude. Conforming cameras detect at least some of these areas; only three contacts are needed to set a light meter for the four most popular film speeds.