Film can only be used once. After that, it cannot be used again (if it is accidentally used again, this results in an artifact called a multiple exposure). When not in use, film needs to be covered from light, otherwise it will record any lights that shine on it. This will make it useless to record a picture. Film comes in a can called a canister to cover it from light rays.
Film needs the right amount of light to make a picture. If the picture is too bright or too dark, it will not record correctly. The longer that the film keeps recording, the more light it will get. If what is being photographed is bright, it will be recorded faster. If it is darker, the film will need more time to record.
Films that need less time to record the picture are known as "faster" films. Different speeds of films are marked with an ISO number. The higher the number, the faster the films.

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