GB477638A - Improvements in or relating to optical projection systems, particularly spot lights - Google Patents

Abstract

477,638. Spotlights and like light projectors. GENERAL ELECTRIC CO., Ltd., and BEGGS, S. S. Oct. 6, 1936, No. 27113. [Class 75 (iv)] A spotlight or like light projector in which the divergence of the beam is varied by variation of the distance between the light source and the optical system, and in which the real or virtual image of the source lies on the same side of the optical system as the source, comprises a diaphragm fixed relatively to the optical system and pierced by a hole so dimensioned and located (1) that, when the beam produced by the optical system is of small divergence, the boundary of the ilhuninated area is not rendered diffuse by the aberrations of the optical system ; (2) that, when the beam is of large divergence, the aperture of the optical system is not materially reduced ; and (3) that, whether the divergence be large or small, substantially no direct light from the source is emitted outside the angle of divergence of the said beam. In the form shown in Fig. 1, the boundary of the hole in the diaphragm 3 lies on the intersection of the rays passing from the source 1<1> to the perimeter 5 of a convex lens 2 when the source is substantially at its least distance from the lens, with the rays passing from the source 1 to the boundary 4 of that part of the lens which gives rise to substantially no aberrations when the source is substantially at its greatest distance from the lens. In the form shown in Fig. 2, the boundary of the hole in the diaphragm 3 lies on the intersection of those direct rays 1-8 from the source 1 which are parallel to the extreme reflected rays 7-6 when the source issubstantially at its least distance from a concave mirror 2, with those direct rays 1<1>-8<1> from the source 1<1> which are parallel to the extreme reflected rays 7-6<1> when the source is substantially at its greatest distance from the mirror. Slight modifications of the position of this last-mentioned boundary are given in the Specification. The hole in the diaphragm is circular or square according to the shape of the lens or mirror.