The original aspect ratio utilized by the motion picture industry was 4:3 and according to historical accounts, was decided in the late 19th century by Thomas Edison while he was working with one of his chief assistants, William L.K. Dickson. As the story goes, Dickson was working with a new 70MM celluloid-based film stock supplied by photographic entrepreneur George Eastman. Because the 70MM format was considered unnecessarily wasteful by Edison, he asked Dickson to cut it down into smaller strips. When Dickson asked Edison what shape he wanted imaged on these strips, Edison replied, “about like this” and held his fingers apart in the shape of a rectangle with approximately a 4:3 aspect ratio. Over the years there has been quite a bit of conjecture about what Edison had in mind when he dictated this shape. Theories vary from from Euclid’s famous Greek “Golden Section”, a shape of approximately 1.6 to 1, to a shape that simply saved money by cutting the existing 70MM Eastman film stock in half. Whatever the true story may be, Edison’s 4:3 aspect ratio was officially adopted in 1917 by the Society Of Motion Picture Engineers as their first engineering standard, and the film industry used it almost exclusively for the next 35 years.
4:3, which the motion picture industry called 1.33:1, was adopted by television beginning in the 1930s.
To compete with TV, movies began experimenting with widescreen aspects in the 1950s — 1.67, 1.85, 2.20, 2.39 (1.85 and 2.39 are the ratios currently used in theaters).
Today’s TVs and computer monitors however, are none of these. HDTV and newer monitors are 1.77 (16:9). A rectangle with that aspect ratio nicely accommodates any of the various motion picture formats (old and new), subject to some letter boxing.