GB535290A - Improvements in or relating to optical systems for or in photographic projection printing apparatus - Google Patents

Abstract

535,290. Photographic projection printing apparatus. ZEISS IKON AKT.-GES. June 27; 1938, No. 19033. Convention date, July 30, 1937. [Class 98 (i)] An optical system for projection-printing apparatus comprises a light source, a condenser system, a projection objective, and two or more means for controlling the state of vibration of light which are relatively movable in order to vary continuously the ratio of the intensity of the light diffused by the negative or original to that directly transmitted by it in the light beam used for the image formation. As shown in Fig. 1, the system may comprise a clear glass lamp L, condenser K, negative holder N, projection objective O and two relatively rotatable polarizing filters, one F in the illuminating beam, and the other F<SP>1</SP> in the imageforming beam. The condenser K forms an image Ll of the lamp L in the diaphragm aperture of the objective O. If an opal lamp or an illuminated matt screen is used as source, the filter F is such that its image, formed by the condenser K, is located in the diaphragm aperture of the objective O, and approximately fills it ; or the two filters F, Fl are located close to the negative. In modifications, (1) the filters F, F<SP>1</SP> are fixed and a rotatable half-wave plate (or two quarter-wave plates) one stationary and the other rotatable) is arranged between them, and (2) the filter F is formed on the envelope of the lamp L, or on one of the elements of the condenser K. In a further modification, using an opal lamp or an illuminated matt screen, the filter F, Fig. 5, is close to the lamp and is surrounded by an annular filter F‹ having its plane of polarization perpendicular to that of F ; and the filter F<SP>1</SP> is disposed as shown, or between the objective O and the light-sensitive sheet P. In this form, an arrangement may be used in which the aperture of an intermediate condenser acts as a light source. Reference is made to the use of elliptically or circularly polarized light, and of devices employing doubly-refracting material. Specification 22671/38 as open to inspection under Sect. 91 is referred to.