A camera used to reduce originals onto film for easy storage. There are two basic types: one in which the film is fixed during exposure, and one in which the film is exposed while moving past an exposing slit. The demagnification ratio may vary from 5x to 30x, and either 35-mm or 16-mm film is used to photograph a flat sheet or a page of a book. Some cameras with mirrors can photograph both sides of a document simultaneously, the two sides being imaged together on the same strip of film. Sometimes a step-and-repeat arrangement is used so that successive pages can be assembled on a sheet of film called a microfiche.