In film terminology, throw is the distance between a movie projector lens and its screen. It is the distance the image is thrown onto the screen, and it has a large effect on screen size.[further explanation needed] Home theatre installations may often have an incorrect[further explanation needed] throw distance in the room but this can be corrected by use of a short throw lens. There are also "long throw" lenses available.
A related measurement, throw ratio, is the ratio of the distance from the lens to the screen (throw) to the screen width. A larger throw ratio corresponds to a more tightly focused optical system.