Motion Picture Herald (Oct-Dec 1955)

FIGURE 8: Approximate shape of a screen image when a rectangular film frame is projected head-on (no projection angle) to a deeply curved screen. FIGURE 9: Approximate shape of a screen image when a rectangular film frame is projected at a steep projection angle (above drawing based on angle of 20 degrees) to a deeply curved screen. FIGURE 10: Approximate shape of picture when a specially corrected film frame is projected at a steep angle (20 degrees) to a deeply curved screen. Film photograph is deformed optically to compensate for aberrations produced by angle and curve. and it of course becomes greater as the angle widens. 1 he problem, which is one of descriptive geometry, can be visualized by drawing lines of intersection between a sloping plane and a vertical semi-cylindrical surface (such as a deeply curved screen forms). This is done in Figure 8, which represents schematically head-on (perpendicular) projection of a rectangular film frame on to a deeply curved screen. In this case, the top and bottom of the film photograph are parallel to the top and bottom of the screen. Although the screen is curved to form a section of a cylinder, the top and bottom edges are horizontal. The only distortion with such non-angular projection is slight fore-shortening at the extreme sides of the screen image due to the fact that they are much closer to the projector than the center. In Figure 9 is indicated what happens when projection is at a vertical angle. The conditions are the same as in Figure 8, except for consideration of an angle of 20°. The screen remains in the same position, and the top and bottom borders appear horizontal. However, the picture from the rectangular frame seems as shown in the drawing — vertical lines lean inward towards the center, and horizontal lines are depressed in the center and lifted up at the ends, so that the horizon appears dished down and convex toward the floor. How deformation of the film photograph can eliminate such distortion of the screen image is indicated in Figure 10. In this drawing the film frame is given a reverse type of deformation, with allowance for keystone and screen curvature incorporated in the film photograph. When this frame is projected at an angle for which its “compression” was calculated, the deformation is cancelled and the picture appears as shown in Figure 10, with vertical and horizontal lines in their proper visual direction and relationship. COMPATIBILITY of ToddAO projection-sound equipment with existing 35mm. systems is completed in a switching-relay-equalizer rack developed for ToddAO by the New York engineering staff of the Altec Service Corporation. According to Altec engineers, the rack provides ready interchangeability between Todd-AO six-track magnetic, CinemaScope four-track magnetic, three-channel Prints with the film photograph shaped comparably to the one drawn in Figure 10, representing “compression” for this purpose, are contemplated in the Todd-AO system. According to Dr. Brian O’Brien of the American Optical Company, the production of these prints involves the entire optical progression of the system, with an important role performed by the printer developed for the system under Dr. O’Brien’s direction. The method implies production of prints variously according to critical ranges of projection angle, with some adjustment available in establishing the screen curvature. reproduction of optical tracks with Perspecta signals, and standard optical recording. The rack contains seven separate panels, with the entire assembly housed in a ventilated heavy steel cabinet having a door to give easy access to components. NO. 1 PANEL This consists in seven magnetic preamplifiers, five for the Todd-AO stage chan Todd-AO Sound System Equalizer Rack BETTER THEATRES SECTION 17