PHOTOGRAPHIC FILTER METHOD AND FILTER DEVICE

摘要

1287883 Printing apparatus; optical filters J L J DASSONVILLE 16 Sept 1969 [25 Sept 1968] 45561/68 Headings G2A and G2J The intensity and/or spectral composition of a light beam 15 is altered by passing the beam through a liquid medium and inserting at least one of a plurality of filters 21-25, 31-35, 41-45, having different densities or spectral absorption characteristics into the liquid medium, the refractive indices of the liquid medium and the or each filter being chosen so as to reduce parasitic reflections. The filters may be grouped as shown and be used in a subtractive colour correction printing method, the filters within each of the three groups differing in spectral density. Alternatively, the printing light beam is split into a blue, green and red beam, and the intensity of each is controlled by density filters before being mixed again. The liquid medium is contained within a rigid housing 10 having light entry and exit transparent panels 11, 12. The filters may be film strips provided with a dyed gelatin layer, and suitable liquids are halogenated hydrocarbons such as trichloroethylene, trichloroethane, perchlorethylene, carbon tetrachloride and corresponding bromine compounds. The filters may be moved manually, mechanically by way of levers, by solenoids or pneumatically in which an air motor for each filter is located outside or within one wall of the housing. Reference is also made to the control of the air motors by a punched program tape. In a modified arrangement, the liquid is contained in a much greater housing and serves other purposes, e.g. biasing a master strip against a photo-sensitive strip during travel past a copying station in a contact printing apparatus.