GB739983A - Light intensity control in optical projection apparatus - Google Patents

Abstract

739,983. Optical projection apparatus. VITARAMA CORPORATION. April 21, 1954, No. 11511/54. Class 97 (1). A projector is provided, in the path between the light source and the transparency, with a grid member composed of slats arranged edgewise to the light beam and rotatable about a transverse axis to intercept varying amounts of light as its angular position is changed. The intensity of the projected image is thereby changed and may be adjusted to match the intensity of an adjacent image in a projected mosaic. Part of one form is shown. A rectangular frame 34 is slotted at 76 to accommodate horizontal slats 38 and vertical slats 74 respectively slotted at 81 and 82 where they cross. The grid is situated in the light beam converging to the film gate and the slats are relatively inclined in cross section to correspond to the convergence of the light beam. The sides of the frame 34 are bowed outward before the slats are fitted so that the slats are kept in tension. The forward edges of some of the slats 38 may be turned up into small flanges in the central region of the projection beam to produce a more even illumination. The grid is carried on pivots in the centres of the vertical frame members and is rotatable by hand or by a reversible electric motor driving through a slipping clutch. The grid rotation is limited by adjustable stops.