GB587493A - Improvements in and relating to optical systems suitable for photography - Google Patents

Abstract

587,493. Optical systems. PHILCO RADIO & TELEVISION CORPORATION. Oct. 13, 1944, No. 19787. Convention date, Oct. 14, 1943. [Classes 97 (i) and 98 (i)] An optical system particularly for use in photography includes a filter comprising a light - transmitting aperture such as to produce a visible diffraction effect, the transparency of the aperture varying as a function of the distance outward from the axial centre thereof. Such a system produces increased contrast in taking or enlarging photographs particularly for use in printing publications. As shown, the filter comprises a transparent disc 1 cemented to partly transparent members 2, 3 of the same refractive index thus forming an annular aperture 4, the diameter d of which is of the order of one-tenth of an inch. The. areas surrounding the aperture may be of gradually varying transparency as shown in Fig. 3 or abrupt, Fig. 11, and the area 2 may be opaque, but is preferably slightly transparent. Fig. 9 shows a projection system comprising a light source 11, condenser 12, transparency 13 and the filter 14, an image being formed at 16 on a ground glass screen or light-sensitive sheet. The filter may be formed by spluttering a glass surface with a thin coating of metal followed, if necessary, by buffing. Alternatively, carbon black may be used and the filter may be applied directly to the image-forming lens.