GB399558A - Apparatus for comparing photographic transparencies - Google Patents

Abstract

399,558. Photometric apparatus. ELECTRICAL RESEARCH PRODUCTS, Inc., 195, Broadway, New York, U.S.A.-(Assignees of Dawson, W. L. ; 233, West 21st Street, New York, U.S.A.) April 8, 1932, No. 10161. Convention date, April 28, 1931. [Classes 97 (i) and 98 (i).] Apparatus for comparing photographic transparencies comprises driving means for simultaneously moving two transparencies through separate restricted beams of light so that con. tinuously changing restricted areas of the transparencies are illuminated, the light transmitted by these areas being caused to fall on two photo-sensitive devices which are differentially connected to an indicator. The invention is particularly intended for comparing the density of the sound record on a kinematograph positive film with that of the record on a standard positive. The film 44 to be tested and the standard film 44<1> are drawn from spools 13, 12 and pass along parallel paths through a cabinet 10 and over drive sprockets 20, 21 to take up spools 26, 27. Within the cabinet is a source of light 42 of such length as to illuminate both films. Light from this source is projected by a lens 50 and reflector 51 on to a slot 52 aligned with the sound track of the film 44, the light passing through the slot and the sound track being incident on a photoelectric cell 54. Light is similarly passed through the sound track of the film 441 on to a cell 55 and the two cells are arranged in a circuit including a battery and a galvanometer 58 in such a way that the galvanometer is deflected when the currents passing through the two cells are different. The galvanometer mirror is illuminated from the source 42 by a lens 56 and reflector 57 and reflects light to a reflector 59 and thence to the scale 60. The light 42 also illuminates a diffusing-screen 43 against which the film 44 can be visually inspected. To prevent injury to the galvanometer when one of the films is removed, each film has a roller 68 pressed against it by a spring 69 so that on removal of the film the roller is drawn forward and closes contacts 70, 71 to complete a short-circuit round the galvanometer. The two pairs of contacts for the two films are arranged in parallel.