Cinemascope
Cinemascope, or more strictly CinemaScope, was a widescreen movie format used from 1953 to 1967. Using anamorphic lenses and 35mm film it could project film at a 2.66:1 ratio, twice as wide as conventional lenses could achieve. It was developed by 20th Century Fox to supplant the complex, multi-projector Cinerama process, first shown in 1952. The actual anamorphic process, initially called Anamorphoscope, was developed by Henri Chrétien around 1927 using lenses he called hypergonar. The hypergonar lens patents were acquired by 20th Century Fox in 1952 and the system was renamed Fox CinemaScope. The advantage over Cinerama was that all the system needed was an additional lens unit fitted to the front of ordinary cameras and projectors, although stereo sound could be carried on separate 35mm tracks. It was first demonstrated in 1953 and the first film shot was “The Robe” (September 1953). The technology was licensed by Fox to MGM and Disney and short-ly afterwards to Columbia, Universal and Warner. However, initial uncertainty meant that a number of films were shot simultaneously with anamorphic and regular lenses. Also only the 'biggest' films were made in Cinemascope, around a third of the total produced.
The 2.55:1 ratio was pretty much dead by 1957 when the last holdout, Fox, adopted magoptical over mag only prints. From that point until the early 1970s a standard of 2.35:1 was used; however, there is usually slight matting in theatres which results in a theatrical aspect ratio closer to 2.40:1. All of the "Star Wars" movies and even the 1997 animated version of "Anastasia" were filmed in CinemaScope, as were classics like "The Robe" and "20,000 Leagues Under the Sea."
SOURCES:
http://en.wikipedia.org/wiki/Cinemascope
http://www.widescreen.org/aspect_ratios.shtml