Patent GB-835705-A (GB)
Title: Improved combined photographic printing and projecting system
IPC: G03B27/68
Filed: 1956-07-30
Abstract: 835,705. Photographic printing apparatus. ABBEY, A. (American Optical Co.). July 30, 1956, No. 23467/56. Class 98(1) As explained in Specification 787,746, if kinematograph film image as shown in Fig. 4 which exhibits barrel distortion is projected by an appropriately located projector on to a cylindrically curved screen the image will appear to an observer, at least near the centre of curvature of the screen, as substantially free from distortion so far as concerns the spacing of objects along the horizontal centre line of the picture. Some curvature will still be seen in vertical objects near the picture margins. To avoid this a film 90 carrying images as shown in Fig. 4 may be printed in the apparatus shown in Fig. 6 on to a film 98, by a lens 92. The films are fed stepwise in the directions of the arrows 93, 95 through gates curved in vertical section. It is shown that the resultant non-uniformity of magnification can be utilized to remove image curvature near the picture margins. A similar apparatus using film gates curved in horizontal section may be used to remove curvature from the regions at top and bottom of the film frames. If, in the apparatus of Fig. 9 the film gates are oppositely tilted about their horizontal centre lines a keystone effect may be introduced into the printed image as shown in Fig. 10. A film 254 carrying such images may be further printed by a lens 260 on to a film 256 in an apparatus as shown in Fig. 16 wherein both gates are concavely curved as about axes 264, 268. This produces a further distortion as shown in Fig. 17, by producing a "droop" of the marginal parts of the picture, which is shown to be necessary when projection is effected from a downwardly raked projector. The apparatus of Fig. 16 also produces an additional keystone effect. The total effect is adjusted to the necessary value 'by adjusting the amount introduced by the first printing step by the apparatus of Fig. 9. In printing with the apparatus of Fig. 16 the horizontal magnification may be adjusted, if necessary, by choosing the relative values radii of curvature of the two gates, the apparatus may be modified to produce the "droop" effect without any keystone effect by inclining the gates in the same direction and disposing them with their convex surfaces facing in the same direction. Fig. 21 shows a continuous feed printing apparatus in which may be introduced all the corrections provided by the printing processes described above. A negative film N and a film P to be printed are fed continuously by sprockets 322, 324 driven at the same speed by the motor 332. A narrow strip 350 of the film N is illuminated by a light beam L and imaged at 352 on the film P by an objective 336, the light path also including an internally reflecting prism 340 containing a plane surface and a prism 338 containing a roof. The film P is guided with a curved cross-section by a suction device 344. The amount of curvature on the image 352 can be varied by tilting the whole optical system, on the frame 334, about pivots 346 the resulting curvature provides the "droop" effect in the final image. While each film frame is printed the magnification may be varied by axial movement of the objective through a pivoted lever 358 actuated by a cam 360 driven from the motor 332. The cam profile may be chosen so that magnification change during the printing of each frame produces the necessary straightening of the picture margins. Keystone effect may also be introduced by the appropriate cam.