The film is available in lengths for varying numbers of exposures. The standard full-length roll has always been 36 exposures (assuming a standard 24×36 frame size). Through about 1980, 20 exposure rolls were the only shorter length with widespread availability. Since then, 20 exposure rolls have been largely discontinued in favour of 24 and 12 exposure rolls. The length of film provided includes the length required for the indicated number of exposures plus sufficient additional length for the film spoiled by being exposed to ambient light when it is drawn out of the canister, across the back of the camera, and securely engaged with the film advancing spool, before the camera back is closed. A camera that uses less than the maximum distance between the spools may be able to make one additional exposure. Self-loading cameras that load the film after being closed don’t spoil the additional length provided for conventional loading and can make that additional length available for two or three additional exposures. The same length can be available for exposures in any camera if it is loaded without exposing the film to light, e.g. in a darkroom or a dark bag. A 27-exposure disposable camera uses a standard 24-exposure cassette loaded in the dark.