Patent GB-862830-A (GB)
Title: Halftone camera
IPC: G03B27/66
Filed: 1957-05-29
Abstract: 862,830. Halftone cameras. EVANS, 0. (Powers Chemco Inc.). May 29, 1957, No. 17046/57. Class 98(1) The camera includes means for accurately adjusting halftone screens of different sizes in a screen supporting frame in precise parallelism with the film supporting frame of a film backing member, and means for maintaining this parallelism once a screen is so adjusted during movement of the screen towards or away from its focus position. In an embodiment of the invention by way of example procedure for circular screens is described first; for this the camera has body 10, bellows 12 and lens 14; and sensitised film or paper may be supplied from roll 16 to be severed by knife 18 for the desired length to be located on to the forward face of backing member 20 preferably of vacuum type and which is movable in the axis of the lens by link mechanism 36, 36, 40 controlled by exterior crank arm 26. Circular screen 22 is mounted for rotation on rollers 91 of rigidly constructed rectangular frame 23 and the latter is held in the screen supporting frame 21 constituted by the majority of the features of Fig. 2. In the latter, side members 46, 48 are connected by widely spaced horizontal members 50, 52 and the side members are provided with laterally extending rollers 54 adapted to roll in trackways 55 in the camera body 10. Secondary side bars 56, 58 rigidly secured in horizontal members 50, 52 have screen supporting cross bars 60, 62 slidably mounted therein and the latter are movable relatively to each other to accommodate screens of various sizes and to centre the screen in the lens axis, chain mechanisms involving cross shafts 72, 77 and chain pairs 76, 81 being provided for this purpose; while four pointers 85 on scales 86 show the positions of cross bars 60, 62. The screen 22 and its frame 23 are first aligned in parallelism with the screen supporting frame 21, and for this a screen frame holding member 95 (Figs. 2 and 6), slidably mounted on lower cross bar 62 by studs 96 receives the lower end of frame 23, and hand nuts 97 are used to urge frame and screen until the latter is in contact with a plurality of aligning plates 101 welded to the rear of cross-bar 62; the upper part of frame and screen are urged similarly by hand nuts 106 against aligning plates 113 welded to upper cross bar 60. The screen supporting frame 21 is movable between a forward or screen loading position and a rearward or screen focusing position by an interconnected gear and rack arrangement (Fig. 3), wherein a pair of upper gears 120 rigidly fixed on a shaft 121 journalled in the camera body and a pair of lower gears 122 rotatably mounted on a shaft 123 are connected by links 124 so that rotation of shaft 121 imparts rotation to all four gears; each gear is in mesh with a rack 125 which racks are attached in pairs to side members 46, 48 of the screen supporting frame 21, three of them being adjustably attached while the fourth is fixed by nut 130. Procedure then is to place the film backing member 20 in focal plane position by lever 26, and to rotate shaft 121 by lever 142 (Fig. 1) to draw screen supporting frame 21 up to the backing member 20 and to adjust the three adjustable attachments until all of the aligning plates 101, 113 are in contact with the backing member 20, whereby parallelism between screen 22 and backing member 20 is attained, and once established is retained during normal manipulation of backing member 20 and screen supporting frame 21 for supplying film to the former and for moving the latter to attain screen distance. Rectangular screen mechanisms are described with reference to Figs. 8, 9 not shown. Specification 751,763 is referred to.