The distortion-correcting printing process was initially meant to be an integrated part of the Todd-AO system. It was originally designed to eliminate three types of distortion, keystone distortion, distortion resulting from using a deeply- curved screen, plus correcting the distortion arising from use of the extremely wide-angle lenses, in both photography and projection.

The above diagram shows why a distortion correcting process, one of the features of the Todd-AO system, was felt to be required. This printing method will counter balance the distortion inherent in projection on a deeply curved screen from steep projection angles. 1A, 1B, 2A and 2B indicate portions of the image striking the four corners of the screen. The lines at bottom must travel further and will therefore spread more than the lines at the top, causing the familiar keystone distortion. Observing line 3 will show that this distortion is even further compounded by the fact that portions of the image striking the center of the screen will always hit lover than portions striking the edge. By means of simple test patterns, an accompanying diagram show how this distortion looks on the screen and how the Todd-AO people plan to correct it.

DISTORTED SCREEN IMAGE

DISTORTION-CORRECTING PRINT

CORRECTED SCREEN IMAGE  

The top section of this drawing shows how straight horizontal and vertical lines are distorted by keystone and screen curvature. Distorting a print in processing so that vertical and horizontal lines would take the shape shown in the film strip at center could counter balance this distortion and provide straight lines on the screen shown at bottom even though that screen be curved. These diagrams are not meant to be an exact description of the Todd-AO corrective printing process. Their purpose is to explain in simple language how it works. In addition to the two types of distortion mentioned above, the Todd-AO method also corrects a print for distortion caused by the use of extreme wide-angle lenses in photography.

Two classes of print were to be produced, one to cover projection angles from 10 to 15 degrees and another for even higher angles. In theory, it was an workable idea, but each type of print was required to cover a range of circumstances. For a perfect system, it would really need to be infinitely variable, producing a print exactly matching each individual theatre. Also, if it was intended to counter-balance the effect of the wide-angle lenses, this part of the correction process would have to be made "switch able", in or out, as the "bug- eyed" lenses were normally only used occasionally throughout the early Todd-AO productions.

The reason for developing this special printing method was largely financial. After his experiences with the high cost of installing Cinerama, part of Michael Todd's brief to the American Optical Company was to avoid the need for major structural alterations and loss of seating, by using a theatres normal projection room, even if this was in its traditional position high up at back of the balcony.

The American Optical Company continued to pursue the idea, right up to the opening of "Oklahoma!". However, the use of an unsuitable print at the premiere did spoil the screen image, judging by these extracts from contemporary reviews from the New York papers.

TRIBUNE, William K. Zinsser:

WORLD TELEGRAM, Altan Cook:

International Projectionist: