Patent GB-945593-A (GB)
Title: Photographic printing apparatus
IPC: G03B27/73
Filed: 1960-01-13
Abstract: 945,593. Photographic projection printing. PAKO CORPORATION. Jan. 13, 1960, No. 1216/60. Heading G2A. [Also in Division G1] General, Fig. 6. An image of an illuminated colour transparency (not illustrated) is formed by a lens 58 on printing material (not illustrated) having emulsions sensitive to red, green and blue light, and a part of the image-forming light is diverted by an inclined plate 62 of optical glass through a condenser lens system 64 to a photoelectric exposure control device (see Division G1) comprising a photo-electric cell (not illustrated) located within a rapidly rotating drum 130 having red, green and blue filters 147R, 147G, and 147B mounted in its cylindrical wall. During printing the photo-electric cell repeatedly and successively samples the red, green and blue components of the image-forming light and produces signals to terminate separately the exposures in each of the: colours. In one way of doing this (as illustrated in Fig. 6) the transparency is illuminated by light from a source containing the three colours and the exposure in any one colour is terminated by introducing a complementary colour filter 195R, 195G, 195B into the light path. In another arrangement, Fig. 14 (not shown), a separate source is provided for each colour and switched off to terminate the exposure. Transparency holder, Figs. 8 and 10. The transparency 100 rests upon a mask 98, below which is located the light source 70 together with heat absorbing and light equalizing filters 91, 92, and is held in position by an apertured clamped plate 101 carried in slots 158 in U-shaped frame 124. The frame is mounted for tilting by a shaft 104 which extends through a bearing 105 secured to the base of the holder. A linkage mechanism 108, 111, 112,113, Fig. 10, permits an operator to raise the frame by a knee pressure against a lever 117. A spring 118 acting on the linkage normally urges the holder into a clamping position, the arrangement being such that the transparency can still be moved in the holder for adjustment. Final clamping of transparency during printing is affected by a solenoid 170 which operates through a lever 172 to allow a further small clamping movement of members 111 and 108 (see Fig. 11, not shown). Printing procedure. The operation of the printer is controlled by a programming circuit, Fig. 13 (not shown), which is started by operation of a foot switch by the operator. The circuit operates the negative locking solenoid (170 in Fig. 10), switches the source of illumination to full brilliancy (normally limited by a series resistor) and releases the circuits of the exposure determining device. After a delay to allow the source to reach full brilliance, a shutter (203 in Fig. 6) is withdrawn from the light path and printing commences. As each colour exposure is completed the corresponding light component is cut off, and at the completion of exposure for all three colours the printer is switched off, the shutter reinserted in the light paths and the printing material (which is in strip form) advanced and numbered. The mechanism for performing this last operation is not described in detail. Exposure control. The exposure control device (see Division Gl) has means for adjusting print density, means for adjusting colour balance without altering overall density, and means for allowing for the difference in transparencies due to flash and outdoor illumination. The device also operates to prevent colour distortion (a shift in the green or complementary colour direction) due to under and over exposed transparencies. Certain of these features form the subject of Specifications 945,597, 945,598, 945,599. The optical arrangement by which part of the image forming light is diverted to the photo-electric exposure control devices forms the subject of Specification 945, 600.