Patent GB-403405-A (GB)
Title: Improvements in or relating to photographic printing apparatus
IPC: G03B27/72
Filed: 1932-06-13
Abstract: 403,405. Photographic printing-apparatus. MoINTOSH, G. W., Inglenook, Lee Grove, Pinner, Middlesex, HEATON, W. E., 119, New Bond Street, and SHORT, S. G., 56, Colwood Gardens, Collierswood, both in London. June 13, 1932, Nos. 16653/32, 16654/32, and 16841/33. [Class 98 (i).] Photographic printing-apparatus comprises in combination a printing lamp the intensity of which can be adjusted, means for holding a negative in the path of rays from the lamp, a test lamp, a viewing screen onto which the beams from both lamps fall, a printing paper holder, a power driven exposure shutter in the path of the light from the negative, means for starting the shutter driving means and an automatic stopping device for the shutter driving means actuated by movement of the shutter or a part moving therewith, after a predetermined exposure period. The printing light and shutter driving means may be electric, the light being then adjusted by means of a rheostat. A ground glass screen may be employed for viewing and similarly tinted e.g. red, screens may be interposed in the paths of the light beams. In the form shown, as applied to a projection printing apparatus, the printing light 13, Fig. 2, is located above a condenser 14 mounted in the upper part of the apparatus. A negative holder is mounted below the condenser and consists of a slide 20, Fig. 4, sliding in guides 18 in the casing and bearing a lower plate 23 held in contact with the slide 20 by a spring 24. The plate 23 carries rollers 28 which, when the slide 20 is pulled to the right, bear against a curved guide 19, and a spring-urged clamping bar 41 for gripping the edge of the negative. A shutter 44 and focusing lens 43 are mounted below the negative holder, the shutter being rotated by an electric motor 49 to make the exposure and being provided with a safelight which is above the lens in the position of rest. Below the lens a mirror 53 is pivoted so as to reflect the light from the lens to the viewing screen. Light from a test lamp 158 fitted with a colour screen similar to the safelight also falls on the mirror 53. The mirror normally occupies the position shown in full lines in which the light from the lens passes to the sensitive surface and is moved into position to reflect the light by a pedal operating through a lever 58 and link 56. The sensitive paper is carried on spools mounted at the sides of the casing and is fed by marginal wheels 66, 67 having pins engaging the paper. The wheel 67 has a fixed flange 69 and the wheel 66 is provided with a disc 70 held against it by springs so as to press on the edge of the paper and retain it in correct alignment. The paper is fed by means of a handle 84 loosely mounted on the shaft 68 carrying the wheels 66, 67. A disc 78 is rigidly mounted on the shaft 68 and locked in position by a spring detent which enters one of a series of holes in the disc. A pin on the handle 84, inserted in a hole in the disc 78 displaces the detent and the disc can then be rotated till the detent enters the next hole. The paper is held in place by a frame 100 which rests on the table 89 over which the paper passes. The table 89 is pivoted about its centre by a link 92 operated by a pedal and is provided with guillotine knives along the edges to cut off the exposed paper. The frame 100 is raised by the tilting of the table 89 and is maintained in raised position by a cam 105 which is manually released by a knob 109 which simultaneously closes an auxiliary circuit of the motor 49 to drive the shutter. The shutter is provided with a notched contact ring in the main circuit of the motor so that the circuit is broken after the shutter has made one revolution. An iris diaphragm may be fitted to the lens 43. According to the first Provisional Specification a pedal may be used to start the exposure by moving the shutter which may be returned by a timing device e.g. clockwork or a fluid-operated dashpot.