GB629179A - Improvements in or relating to kinematograph projection with continuously moving film - Google Patents

Abstract

629,179. Kinematograph projectors. SCOPHONY, Ltd., WIKKENHAUSER, G., ADAMS, A. E., COOK, G. H., and DUGGAN, R. E. Dec. 16, 1946, No. 37075. Addition to 589,971. [Class 97 (i)] A kinematograph projector as in the parent Specification comprises a number of optical compensators equal to or one less than the number of light flashes per frame, each of said compensators being mounted for rotation about a single axis. As shown in Fig. 1, a film is continuously moved by a rotatable sprocket 4 mounted on a shaft 5 geared to a shaft 7 carrying a prism 6. An electric discharge lamp 1, associated with which is a lens system 2 and a rotating disc 11 having a slot 12 therein, is caused to illuminate the film by two light flashes per frame. In order to compensate for the film movement between successive light flashes, the hypotenuse face of prism 6 is caused to deflect the light through the projection system 10 twice per frame, the prism taking up the position shown in the full and broken lines, Fig. 2, respectively. The film having moved through a distance d, the length of the light path is changed; the prism is designed to compensate for the defocusing which the change would otherwise produce. Instead of the single prism, a prism and a mirror, which is parallel to the reflecting face of the prism, may be rotatable about a common axis, or a group of prisms and mirrors rotatable about an axis parallel to their reflecting faces may be used; the prisms in this case are each designed to compensate for the defocusing which would otherwise be produced by the change in length of the light path. Two mirrors 16, 17, rotatable in their own planes about a common axis 18, may be used, as shown in Fig. 3, one mirror being operative for each light flash. In order to prevent defocussing when mirror 17 is operative, a parallel-sided glass block 21, also rotatable about 18, is used; this block may, however, be mounted for rotation about an axis perpendicular to the projection axis. In another case, a prism and a mirror are disposed side-by-side so as to be slidable into and out of the light path to render one or other of them operative.