GB313634A - Improvements in or relating to optical apparatus for projecting illuminated signs upon screens - Google Patents

Abstract

313,634. Randall, C. E., Thompson, L. R., and Savage, J. C. Dec. 14, 1927. Optical-projection apparatus.-Luminous signs &c. are projected on to clouds or other distant screens, without the use of a stencil or other facsimile of the sign &c., by means of a projector producing a definite beam and an assemblage of variously-tilted mirrors occupying an inclined cross section of the beam. As shown in Fig. 6, a housing h, containing a searchlight reflector and a light source, arranged to produce a substantially parallel beam, is mounted, in conjunction with a mirror board c, on a base g carried by a turntable @ circularly adjustable on a bed p mounted on a carriage q. The mirror board is inclined to the axis of the beam and carries a number of mirrors M, Fig. 3. The mirrors are universally adjustable, and the adjusting means may comprise ball and socket mounts b and screws d, or tension springs e and screws d. The screws d may be replaced by rods projecting through the board c and capable of being engaged by screws or other adjustable devices on interchangeable boards which may be separately applied to the back of the board c to set the mirrors so as to produce predetermined signs. Alternatively, the mirrors may be set by means of cam surfaces moved past the rods secured to the mirrors. The light source may have an aperture plate in close proximity to it to produce, uniformity of outline' and illumination in the luminous spots projected by the various mirrors. The aperture plate may have an aperture of square, hexagonal, or other regular shape, or. of a fanciful shape such as the shape of a letter or character, and may be cooled by the circulation of a fluid through it, as described in Specification 291,826. A construction of apparatus is described comprising opposed projectors having two mirror boards between them which co-operate to produce a single display. Prisms or lenses may be substituted for mirrors in the apparatus, where practicable, and moving or revolving mirror assemblages involving the principle of persistence of vision may be used in the apparatus. According to the Provisional Specification, a divergent beam of light may be passed through a perforated plate to produce separate diverging beams, each of which may be directed by a concave mirror or lens directly on to a screen to produce a desired sign, or on to a plurality of independently adjustable mirrors for the same purpose.