While high definition has brought with it some standardization of video aspect ratios, there are several legacy formats still in use from the days of film. These are dependent on the film gauge and shooting format used to capture the footage.
35mm full frame utilizes the space between perforations on standard 35 mm film stock and has an aspect ratio of 1.33:1.
The Academy Ratio is slightly wider at 1.375:1, most popular between 1932 and 1952.
1953 saw the creation of Cinemascope, an anamorphic lens that squeezed a widescreen format of 2.66:1 onto a 35mm gauge film.
Super 16mm uses a smaller film gauge and has a wider aspect ratio at 1.67:1, making it easier to transfer to widescreen formats.
Vistavision is a larger format, captured sideways on the film and is mainly used in special effects work.