Patent GB-1072774-A (GB)
Title: Photographic multicolour printing
Inventor: NEALE DENIS MANKTELOW
IPC: G03B27/73
Filed: 1964-07-17
Abstract: 1,072,774. Photographic colour printing. ILFORD Ltd. Oct. 13, 1965 [July 17, 1964], No. 29360/64. Heading G2A. In printing from a multicolour transparency, the photo-sensitive material is exposed to light of three different qualities in turn, in any sequence, light of the first quality comprising light in bands a and c of three Spectrum bands but not band b, light of the second quality comprising light in bands b and c but not a, and light of the third quality comprising light in one only of said bands. In one form, a yellow, cyan, or magenta filter is placed in the path of white light, then another such filter different from the first, and finally another filter which restricts printing light to one of the three additive primaries red, green, or blue. The filters may form sectors of a disc, as shown in Fig. 1. Sector 1 is magenta, sector 2 is yellow, and sector 3 is an additive primary which may for example be red. Sector 4 is opaque. These four sectors subtend respective angles #1, #2, #3, #4 at the centre of the disc. Two further opaque sectors 5, 6, subtending angles #5, #6 are pivoted at the centre of the disc, and can be secured in any position. Thus the overlapping angles #x, #, can be adjusted to a desired value. The disc rotates continuously, and it is shown that the proportions of blue and green light transmitted can be brought into a desired ratio by adjusting #x, and the relative proportion of red light adjusted by adjustment of #y. Fig. 2 (not shown) is a modified arrangement in which the filter sectors can be brought to rest in the path of the light beam for adjustable controlled time. In this form, filter sectors (7, 8, and 9) correspond to sectors 1, 2, 3 of Fig.1. The disc (10) carries a bar magnet (NS1) which causes red switches (S7, S8 and S9) to open in turn as the magnet is carried past them. The movement of the disc is controlled by the timing circuit of Fig. 3 (not shown). This comprises an arrangement of resistance-capacitance elements, each controlling a respective cold cathode trigger tube (V1, V2, V3) so that the disc is rotated to bring each filter into the light path for a predetermined time dependent on the values of the circuit elements. An alternative circuit arrangement utilizes three photo-electric cells with corresponding filters, which act as photo-electric integrators. The Fig. 2 arrangement suffers from the limitation that the exposure time to red must at least equal the sum of the exposure times to the other two colours. Fig. 4 (not shown) is a further arrangement which avoids this limitation. Disc (10) comprises the same filter sectors (7, 8, 9) as in Fig. 2. Also in the light path (11) is a second disc having an opaque sector (13), a sector (14) transmitting all colours, and a cyan (i. e. redabsorbent) sector (15). Fig. 5 (not shown) is a diagram of the controlling circuit, The "standby" position has sectors (7 and 13) in the light path. On pushing a starting button, disc (12) rotates to bring sector (14) into the light path, so that exposure to blue and red light takes place. After sufficient exposure to blue light, disc (10) is rotated to bring sector (8) into the light path (blue light ceases, green light commences, red light continues). Further rotation of disc (10) brings red sector (9) into the light path. Cyan filter (15) also rotates into the light path, and if either blue or green exposure is incomplete, it remains there. When exposure to all three colours is complete, the discs are rotated to the "stand-by" position once more. Tables are given listing combinations of colour filters other than those given in the above examples.