Patent GB-506540-A (GB)
Title: Improvements in or relating to photography in relief
IPC: G03B35/24
Filed: 1937-11-30
Abstract: 506,540. Stereoscopic photography; projection screens. LASSUS ST. GENIES, A. H. J. DE. Nov. 30, 1937, No. 33124. Convention date, Dec. 16, 1936. [Classes 97 (i) and 98 (ii)] A lenticular screen for use in association with an objective, for example a principal view-taking objective, in photography in relief comprises a first divergent optical system consisting of one or more networks, the system producing virtual images of the exit pupil of the objective and a second optical system consisting of a network of convergent elements directing the rays emanating from the centres of said virtual images on to a point situated on the side of the screen remote from the objective. A first network of divergent lenses may form substantially in its focal plane on the side facing the objective, a multiplicity of small virtual images on the exit pupil of the objective, and a second network of convergent lenses may be arranged on the side of the first network remote from the objective, the second network being arranged at substantially its focal length from the plane containing the small virtual images, the centres of the lenses of the second network being aligned with the centres of the small virtual images and a point situated on the optical axis of the complete system on the side of the screen remote from the objective. As shown, O is the objective of a projector or of the primary chamber of a camera. The screen E comprises a first divergent network E1 of focal length f and at the top of the figure, a second convergent network E2 of focal length f2. The element of optical centre e1 gives a virtual image i1 of the exit pupil of 0 in the plane II which coincides substantially with the focal plane of E1, and a real image of this virtual image is formed at H by the convergent network E2. H may be the entrance pupil of the objective of a secondary chamber, or the objective of one of several secondary chambers, recording the image in relief on a lenticular film. If one at least of the networks E1, E2 comprises cylindrical optical elements the zone H is extended. At the bottom of Fig. 1 is arranged between the networks E1, E2 a convergent echelon lens D of the Fresnel type. If one or both networks E1, E2 are cylindrical, the network D may comprise convergent cylindrical elements. Stopping down of the elements of El may be effected by a grid integral with El. In a modification the elements of E1 may comprise divergent menisci and those of E2 convergent menisci, the convexity of both being directed towards O. The elements of each network are different fragments of lenses of a given type the same throughout in each network, and the fragments differ progressively as the distance from the principal axis increases, and the arrangement is symmetrical about this axis. The elements of the two networks may be joined by partitions or a grid may be arranged in front of the first network. In another modification the first divergent network may be replaced by a first convergent and a second divergent network. The third convergent network may be omitted. Each network may comprise several constituents with elements of appropriate curvature and indices. One or more networks may comprise spherical optical elements and the others, cylindrical elements. A glass plate with parallel faces may be osci!- lated near the objective of a secondary chamber to remove moirÚ. Specification 455,220 is referred to.