With the unprecedented sale of DVD players and the availability of so many films transferred in wide screen formats, there are countless discussions of ORIGINAL ASPECT RATIO. There are also countless experts on the subject, most of whom know nothing of what they speak. The subject is a lot simpler than most people believe, and being a simple kind of guy, I'll spell things out for you.The CinemaScope Aspect Ratio
ASPECT RATIO WHAT THE TERM MEANS: Aspect ratio refers to the relationship in size between the height and width of an image. It must be remembered that this is a SHAPE. It has nothing to do with content.
1953 - 2.66:1. During the developmental period of CinemaScope, and before it was in any way certain that it would be possible to put the stereophonic soundtracks on the same film as the picture, CinemaScope used a conventional film with an aperture size identical to the original silent film aperture. This format uses the absolute maximum available area on the film to provide optimum image quality. The sound was carried on a separate full coat 35mm magnetic film that ran in interlock with the picture projector. Warner Bros' Warnersuperscope, (which never really got off the ground), and Carl Dudley's short lived Vistarama both also conformed to the same 2.66:1 ratio with interlock sound.
1953 - 2.55:1. By the time The Robe was ready to premiere, 20th Century-Fox had solved the magnetic stereo sound problem on the picture film with the able assistance of Cinerama sound guru Hazard Reeves. Adding the four small bands of magnetic oxide required the use of smaller perforations and a slight reduction in the width of the picture.
1955 - 2.35:1. Exhibitor resistance to investing in stereophonic sound reproduction equipment forced the use of several different sound formats for CinemaScope. There was a mono magnetic sound stripe that was located in the same area as the optical soundtrack in standard films and there were optical mono soundtracks as well. In addition, MGM utilized the crummy Perspecta system to create ersatz stereo effects. These formats used standard film perforations and necessitated a reduction in image width to yield 2.35:1. In 1957, with the adoption of the magoptical sound track, which incorporated both a narrow optical mono soundtrack along with the four magnetic stripes, finally eliminated 2.55:1 as a ratio for CinemaScope and other anamorphic 35mm systems.
1970 - 2.39:1. The height of the CinemaScope image on film, (and all other clone systems), leaves no room between frames. Consequently, splices, both done in the lab and and in the theatre, would cause flashes of light at the top or bottom, or both, of the picture. Theatres took to masking the 2.35:1 frame down slightly to cover the splices. In 1970, the SMPTE set an "official" standard that reduced the height of the projector aperture to conform to the general practice that had been in use for several years. While 2.39:1 is a wider ratio than 2.35:1, the change represents a reduction in height not an increase in width. The difference in shape is inconsequential and thus the aspect ratio of anamorphic films is interchangeably referred to as either 2.39:1 or 2.35:1. This change represents no change in the production of the film, it's a change that is done in the theatre projector and screen masking.
This ratio applies to all present day 35mm 2x squeeze anamorphic prints, be they originated in CinemaScope, Panavision, Technirama, Tohoscope, Super 35 or any other clone of the CinemaScope standards set in the 1950s.