GB386879A - Improvements in or relating to optical instruments arranged to provide a diffusely illuminated testing or exposure area - Google Patents

Abstract

386,879. Photographic apparatus. ELECTRICAL RESEARCH PRODUCTS, Inc., 195, Broadway, New York, U.S.A.- (Assignees of Eich, F. L., 627, North Plymouth Boulevard, Los Angeles, U.S.A.) June 23, 1932, No. 17792. Convention date, Jan. 5. [Classes 97 (i) and 98 (i).] A method of compensating for irregularities in the illumination provided by optical instruments comprising a source of illumination arranged to provide a diffusely illuminated testing or exposure area, consists in exposing an area of photosensitive material in the light path between the source of illumination and the testing or exposure area, removing and treating the photosensitive material to give. a photographic transparency of which the light transmission is substantially inversely proportional to the intensity of the light incident on the photosensitive material, and positioning the photographic transparency in the light path between the source of illumination and the testing or exposure area in effectively the same position as that previously occupied by the photosensitive material. As shown is Fig. 1, a cabinet 1 encloses a source or sources of light 2 partially surrounded by a reflector 3, the light being diffused by the screen 4 and falling on a glass sheet 5 in an opening in the top of the cabinet 1. On sheet 5, Fig. 3, is a sensitometer strip 6 having areas with different light transmission characteristics, partially masked by the opaque sheet 7 and covered by the transparent sheet 8, on which the section of photographic material to be tested, such as a piece of kinematographic film, is held by the pad 10. A piece of photosensitive material 11 is placed on the glass sheet 5 and gives the correct exposure. It is developed in a non-staining developer to a gamma of approximately unity, washed, fixed, and dried. The exposed material 11 is then replaced under the glass sheet 5. Alternatively the reflector 3 may be coated with photosensitive emulsion and treated in a similar manner. The method may be applied to photographic enlargers, sensitometers, densitometers, or photometric apparatus.