Motion pictures were originally made with strips of plastic called film (or film stock). In 1885, George Eastman and William H. Walker invented the first strips of film. Today directors can easily shoot with digital cameras since film is expensive. There are different widths of film. 8 mm and 35 mm are generally used for theatrical productions. Each square is called a frame, and once the film is projected it looks as if the subjects are moving (thanks to the persistence of vision).