Special film holders and accessories can fit in place of standard film holders for specific purposes. A Grafmatic, for example, can fit six sheets of film in the space of an ordinary two-sheet holder, and some light meters have an attachment that inserts into the film holder slot on the camera back so the photographer can measure light that falls at a specific point on the film plane. The entire film holder/back assembly is often an industry standard Graflex back, removable so accessories like roll-film holders and digital imagers can be used without altering focus.