GB824977A - Colour filter device and photographic printing apparatus embodying the same - Google Patents

Abstract

824,977. Photographic printing apparatus. ILFORD Ltd. Jan. 20, 1958 [Jan. 31, 1957], No. 3438/57. Classes 98(1) and 98(2) [Also in Group XXXV] For colour printing or use with variable contrast black and white material, the apparatus has a source of light changing between maximum and minimum brightnesses at a high cycle frequency filtered by passage through an element made up of uncoloured and coloured areas which is introduced intermittently at a frequency related to the cycle frequency of the source by an integral factor and means for adjusting the relative phase relationship between the source and the filter element. The source may be a gaseous discharge lamp, and the filter element one with coloured areas as of yellow magenta or cyan and also uncoloured areas for reciprocating passage or operation as a rotating disc. As shown there are two such discs 8, 9 with coloured sectors 10, 11 and 12, 13 driven motors 14, 15 respectively in the path of light from discharge lamp assembly 1, 2, 3 through condenser lenses 4 transparency 5 and objective lens 6 to print material 7, the same alternating current supplying both motors and lamp, and adjustment of phase relationship of each filter disc can be effected by rotation of the housing of the motor which drives it. The colour of sectors 10, 11 differs from that of 12, 13. Maintenance of the ratio of blue green and red light at a predetermined value by using monitoring photocells each controlling one colour and arranged to control via servomotors the angular position of the rotating discs is indicated.