The renewal of interest in 50mm film at Fox in 1944 was motivated, in part, by experiments with optical stereophonic sound in the early 1940s. From 1939 to 1940, Dr. Harvey Fletcher of Bell Labs conducted experiments on a three-channel stereo sound system (Wysotsky, 1971). In 1940, Disney released Fantasia in a limited-run, double-system format called Fantasound, with three separate sound tracks. At around the same time, Warner Bros. experimented with a process called Vitasound in which sound effects and music on a single track were spread to different speakers around the theater (Handzo, 1985). At Fox, Lorin Grignon continued Fletcher's experiments, perfecting methods of recording stereo sound suitable for film production (Grignon, 1949). By using 50mm film, Fox engineers were able to place three channels of stereo optical sound alongside a widescreen image, eliminating the double system format employed by Disney.

Starting in January 1944, Fox conducted a series of tests in conjunction with Western Electric (Electrical Research Products, Inc.) and Eastman Kodak Co. on both B/W and color 50mm film stock, using stereo optical sound. Using a converted Movietone News camera, E. I. Sponable, director of research and development at Fox, filmed scenes of New York Harbor, the George Washington Bridge and Niagara Falls. (Anon., 1945). By December 1945, Fox had agreed to shoot a more extensive demo film based on a short script set in the Civil War era called The Clod. Written by Dorothy Bennett, photographed by Joe McDonald and directed (gratis) by Henry King, the film was budgeted at $15,000 and came in at $25,000 (Klune, 1945). The film, and the 50mm shorts that accompanied it, were designed to sell Fox executives on 50mm film and stereo sound.  

An initial demo was held in Hollywood on 25 June, 1946, to which Fox executives and engineers working at other studios were invited. The International Projectionist described these tests as an “effort to neutralize the competitive threat of 16mm home movies and television.” (International Projectionist Publishing Co., 1946). The non-fiction demo footage involved switching back and forth between 35mm B/W monaural footage and 50mm color stereo sound footage. Columbia's John Lividary praised “the photography of events too large for the regular screen to digest” and noted that “with color, these scenes would have terrific public appeal”. He continued, in language that foreshadowed Cinerama, that “pictures capitalizing on this ability of the wide film by bringing to the screen scenes of natural beauty that the present medium is incapable to properly represent would offer new and desirable elements of enjoyment" (Lividary, 1946).

Loren Ryder of Paramount noted that the stereo sound was quite effective, “especially when we heard off-stage sounds from both right and left screen”. “Your group is to be congratulated,” he wrote, “on the microphone technique which … for the most part avoided apparent movement of the characters when they looked right and left. This technique also minimized the echo effect which has been heard in most stereophonic pick up." However, Ryder was critical of what he called “picture breathing”, or buckling in the gate, and “color fluctuation”. He also complained that with the wide film display there was no specific focus to the shot – only a “universal” focus (Ryder, 1946). However, he found the optical stereo sound flawed by “ground noise” and “heavy” frequency response characteristics (Lividary, 1946).

Another demo was held later that year, in Hollywood in October. It was specifically for Fox executives and was discussed in an internal memo that reflects the disappointment on the part of the engineers in the executives’ response: “October 25, 1946. Held demonstrations for Skouras, Michel, Adams, officials of ERPI, Eastman Kodak, Joe Schenck and others, in Grandeur projection room at Western Avenue, Hollywood. (Mr. Zanuck did not choose to attend this demonstration.) The conclusion expressed by Schenck was that the motion picture business was so good that it was difficult to serve the theatres with 35 mm. product so why get into something new? Skouras said if executives on the Coast did not support the program it should be tabled.” (Sponable, 1956)

In his history of the development of CinemaScope, Herbert Bragg made a similar comment about the response of Fox executives, noting that, at the time, 50 mm “had been brushed off by certain executives of the Company as non-commercial” (Bragg, 1988). Lorin Grignon echoed this sentiment in a letter he wrote to Sponable in 1956, recalling work leading up to the development of CinemaScope. Referring to a meeting in October 1952 called by Fox executives to discuss the success of Cinerama, Grignon wrote, “You described in some detail, the results of our 50mm experiment using an aspect ratio of 1.8 to 1 and stereophonic sound. As I recall, you also mentioned that even though the experiments were considered highly interesting and giving a new face to motion pictures, that no one, even in our own Company, cared to proceed with these innovations and therefore, the investigations were terminated." (Grignon, 1956).

Sponable persisted in viewing 50mm film as the ideal format for widescreen cinema. When Sponable first viewed Cinerama in a converted indoor tennis court in Oyster Bay, Long Island, he noted that he was “not impressed with its commercial possibilities as compared to our own wide film systems” (Sponable, 1956). In another memo, Sponable noted that Cinerama “has many technical limitations and is of no interest to Twentieth Century-Fox in its present form. The work we did on 50 mm. film in an experiment performed on the Coast a few years ago is a much more practical approach to the problem of making wide angle pictures with stereophonic sound.” (Sponable, 1956)

Because of their prior work with 50mm film, Fox engineers knew that whatever widescreen system they chose to develop would have to be compatible with existing theatrical equipment. In the early 1950s, Fox executives rejected 50mm (possibly because its aspect ratio was only 1.8:1 as opposed to Cinerama’s 2.65:1 – i.e., the format was significantly less wide than that of its competition). When Fox president Spyros Skouras and Sponable selected Henri Chrétien’s anamorphic Hypergonar lens, Fox engineers viewed it as the basis for a spectacular widescreen system that, like 50mm film, was essentially compatible with existing 35mm theater projection equipment and that could generate an image of near-Cinerama proportions with an (initial) aspect ratio of 2.66:1 that was subsequently reduced to 2.55:1 when the projection format shifted from double-system to single-system at the time of the release of The Robe (September 16, 1953).