GB541753A - Improvements in or relating to optical systems composed of lenticules - Google Patents

Abstract

541,753. Optical systems ; projection screens. GABOR, D. May 3, 1940, No. 7983. [Class 97 (i)] An imaging system comprises two arrays of cylindrical lenticules. 9, 10 having parallel axes and on opposite sides of a single sheet or of two sheets joined in optical contact, the spacings of the lenticules in the two arrays being different, and neither an integral multiple of the other; the separation of the arrays is equal to the algebraic sum of their focal lengths fa, fb, if both the arrays are transmitting or, is one of the arrays is reflecting or backed by a plane reflector, is equal to the algebraic sum of twice the focal length of the reflecting lenticules and the focal length of the others. The spacings of the arrays may be in the ratio of two prime numbers having a difference which is small compared with them. The Specification demonstrates that the arrays are equivalent to " superlenses " causing parallel incident light to emerge in parallel or nearly parallel bundles which unite to form " superfocal " lines much smaller in number than the lenticules in the arrays ; under certain conditions only one " superfocus " is formed. Complete particulars for a moulded polystyrene plate capable of concentrating solar energy in a focal line 1.8 metres from the plate, to heat liquid in a tubular boiler, are set out in the Specification. If the energy is to be concentrated approximately to a point, two plates having lenticules at right angles to one another may be used, or the lenticules may be formed as concentric toroidal ones. Other uses comprise condenser lenses, lighthouse lenses, part of projection screens according to Specification 541,751, and as members of projection systems of wide aperture for stereoscopic projection as described in Specification 541,752; examples of projection systems embodying such plates, and serving to enlarge the projector aperture, are described. The lenticular arrays form the equivalents of large lenses without using so much material, and permit the possibility of imitating very large or very small refractive indices, with the result that magnifications are produced which are not in the ratio of image distance to object distance. Manufacture may be effected by assembling ribbons shaped by rolling plastic materials between geared profiled rollers, or by assembling small rectangular sheets moulded by two plates set in a jig, the plates being relatively and progressively moved to be suitable for different parts of the built-up sheet. The ribbons or small sheets may be held between glass plates or in metal frames. The complete sheet may be composed of glass, or of various plastic materials, or of sheets of different refractive indices joined in optical contact at an interface which may be rendered diffusing, and may also be curved about an axis parallel to the lenticular axes ; its lenticules may be all convex or convex on one side and concave on the other. Specification 506,540 also is referred to.