Patent GB-518174-A (GB)
Title: Improvements in and relating to cinematograph apparatus
IPC: G03B41/08
Filed: 1938-08-16
Abstract: 518,174. Kinematograph apparatus. EISLER, P. Aug. 16, 1938, No. 24147. [Class 97 (i)] In continuous-feed apparatus wherein the compensator consists of one or more tilting plane reflectors wholly outside the objective system, tilting is effected by mechanism comprising members which wholly determine the law of tilt as a function of the film displacement and other members which wholly determine the amplitude of tilt; the amplitude may be adjustable to meet variations in focal length of the objective, projection throw, screen size &c. Fig. 7 shows a projector wherein the light patch on a continuously moving film 1 is moved with the image by a spiral slot in a rotating disc 59, and compensation is effected by a reflector 3 which is tilted while being moved through the beam and reflects to a mirror 4 and thence to the projection screen 5. The reflector 3 may be one of a series moved in a closed path, which is rectilinear while the reflector is effective, and is parallel to the top surface of a casing 50 containing operating mechanism driven from the projector by a chain and chain wheel 55 on a shaft 52; the lower part of the casing may form an oil sump. The reflectors 3 are mounted in carriers 22, Fig. 4, pivoted on pillars 17 and carrying long levers 23. The pillars 17 are secured to endless chains 7, 8 running on sprockets 9, 10, the sprockets 9 being on a shaft driven by bevel gearing 16 from the shaft 52. Grooves in a base 13 respectively guide the bottoms of the pillars 17 and pins on brackets 20 extending from the pillars. The levers 23 are formed with cams 24 slotted so as to be engaged by pins 26 extending from blocks 25 sliding, at uniform speed while the mirrors are effective, on the pillars 17; the cams determine the law of tilt, and their form is deduced in. the Specification. The blocks 25 carry other pins 27 producing the sliding movements by engagement in a normally fixed guide 28 which forms a closed circuit and is straight where it effects the compensating movement; the guide 28 determines the amplitude of tilt, and means is described whereby its slope may be varied to change the amplitude. A moving band co-acting with the mirror 4 may be used for masking. Figs. 9 and 10 show a modification in which an endless band comprises five flexible mirror portions 61 running over drums, each portion tilting about axles 63, parallel to its direction of movement, for compensation. The law of tilt is determined by a system of levers 69, based on principles set out in the Specification, and duplicated at the ends of each portion 61 to operate thereon through pins 71a, 71b. The levers 69 carry rollers 73 running in guides 74, Fig. 10, which, in their inclined effective portions determining the amplitude of tilt, are straight; the inclined portions of each guide may be variable in inclination, and is connected by flexible parts 77 to the remainder of the guide. Each mirror portion 61 may be blackened as indicated in Fig. 9 to render other masking unnecessary, and the ends of each portion may be shaped to produce a dissolving effect between successive projected images. A further modification is described in which reflectors tilt about axles extending between parallel endless chains,- and are tilted by followers riding over adjustable cams. Means for deviating the whole light beam so that it follows the film image are described. As shown in Fig. 17, the means comprises a rotatable annular prism 105 of changing section, producing a deviation of gradually varying angle and a rotatable spiral prism 106 of variable section such as to direct the beam into the projection lens C. In modifications, a rotatable spiral reflector or a helical reflector, each of curved section, may be used.