GB939219A - A method and apparatus for the production of photographic colour prints - Google Patents

Abstract

939,219. Photo-electric control of photographic printing. AGFA A.G. Feb. 16, 1960 [Feb. 20, 1959; Jan. 30, 1960], No. 5530/60. Class 40 (3). [Also in Group XX] A method of photographic colour printing comprises exposure to white light until the exposure to one primary colour component is complete, followed by the sequential insertion into the printing beam of filters of the two remaining primary colour components to complete the exposures to these colours. White light from a lamp 1, Fig. 1, passes through a condenser 2, 3 and a colour transparency 4 to a printing surface 7. Light passing through the printing paper is reflected from a mirror 10 to the photo-cells 11, 12, 13 through blue, green and red filters 14, 15, 16. Green, blue and red filters 17, 18, 19 and a shutter 29 are arranged for insertion into the printing beam. Printing is initiated by actuating a switch 75, Fig. 4, momentarily energizing a relay 74 to break contacts 74a, 74b, 74c and cutting off thyratrons 49, 50, 51. Relays 52, 53, 54 are de-energized, breaking contacts 52b, 53b, 54b and de-energizing the relay 73 which operates contacts 73a to open shutter 29 and 73b to increase the printing lamp intensity from an inspection to a printing value. The photo-electric current through cells 11, 12, 13 charges condensers 61, 62, 63 until one, say 61, reaches the potential necessary to reignite its thyratron. Relay 52 is then energized and contact 52a completes the circuit of relay 23 to insert the filter 17. When thyratron 50 strikes contact 53c closes and 53d opens to replace filter 17 by the filter 18. Exposure continues until thyratron 51 strikes closing the circuit of relay 73 to close shutter 29. In a modification, Fig. 5, a semi-reflecting plate 81 in the printing beam directs some of the printing light to the photo-cells via interference mirrors 82, 83.