GB535289A - Improvements in or relating to optical systems for or in photographic projection printing apparatus - Google Patents

Abstract

535,289. Photographic projection printing apparatus. ZEISS IKON AKT.-GES. June 27, 1938, No. 19032. Convention date, July 30, 1937. [Class 98 (i)] An optical system for projection printing apparatus comprises a light source, one or more condensers, a projection objective, and two or more stops, screens or filters which are relatively movable in order to vary continuously the ratio of the intensity of the light diffused by the negative or other original to that directly transmitted by it in the image-forming light beam, the stops &c. being so disposed that they influence only the contrasts of the image, and not its size. The stops may be formed of opaque material, or of material which wholly or partially absorbs the photo-chemically-effective light while transmitting visible but photochemically-inactive light; and they may be located in front of or behind the negative or original. As shown in Fig. 1, an image L<SP>1</SP> of a source comprising a clear glass lamp L is formed near the projection objective O by a condenser K, and in front of the negative N relativelyrotatable stops F, F<SP>1</SP> are located near the image L<SP>1</SP>. The stops may take the form shown in Fig. 4. As shown in Fig. 3, a clear glass lamp L illuminates the matt surface Km of a condenser K<SP>1</SP>, an image of which is formed near the projection objective O by a second condenser K<SP>2</SP> in front of which the negative N is located. The relatively-rotatable stops F, F<SP>1</SP> are located in this case between the elements of the condenser K<SP>1</SP>, and may take the form shown in Fig. 6, F comprising a part similar to F<SP>1</SP> and an annular surround Fo. Similar stops may be used in a system resembling that of Fig. 1 but using an opal lamp. The stops may alternatively be of chequer pattern, either rotatable or laterally displaceable relatively to each other. Specifications 535,290 and 22671/38 as open to inspection under Sect. 91 are referred to.