Phototypesetting is a method of setting type with light (photo). It consists of a character matrix in the form of film negative, which has the images of all the characters, a light-sensitive paper and a light source. The characters in the matrix are exposed to the photographic paper by the light source through a lens one by one as they are typed in the keyboard, in a similar way to that of typewriters. The exposed photographic paper is developed and used as master for reproduction of plates, which is required for the printing process offset lithography. The difference in fonts are achieved by each character matrix for every font. The difference in size of the character is achieved with the lens unit.
History
The genesis of phototypesetting dates back to 1940s and it became popular in early 1970s, when it replaced metal typesetting, with the growing popularity of offset lithography. Phototypesetting was later superseded by imagesetters and laser printers.