GB568274A - Improvements in or relating to photographic enlarging apparatus - Google Patents

Abstract

568,274. Photographic enlarging apparatus: ROGERS, G. H. Aug. 5, 1943, No. 12659. [Class 98 (i)] In photographic enlarging apparatus for use with lenses of different focal lengths in which the projector head and the paper holder are relatively movable and in which means operated or controlled by the movement automatically adjust the focusing devices of the projector to maintain any of the lenses at its correct focus for any setting of the enlarger, the projector head is movable along a support and carries a pinion rolling on a rack fixed to the support as the head moves along the support, a cam being rotatable by the pinion and engaging a cam follower mounted on a lever connected by links to the focusing device of the projector lens and the cam having a contour adapted to maintain the lens in focus throughout the range of movement of the projector and being replaceable by appropriate cams for the other lenses of the set. The means for adjusting the focus may comprise a member (e.g. a cam) coupled or geared to the moving part of the enlarger and connected to the lens mount by levers, links, or the like, adapted to move the lens. As shown, the projector head has horizontal supports 6 provided with guides so that the head may be moved manually up or down the vertical cylindrical column 7 against a counterweight attached to a chain passing over sprockets or pulleys at the top of the column. The counterweight moves between guide rails also serving to guide the supports 6. The head is moved by a hand wheel 12 operating a pinion engaging a rack fixed to the column or operating a sprocket wheel 16 engaging a taut chain 15. Levers 17 pivoted near the column are pivoted to links 18, the free ends of which are joined by a crossbar 19 coupled by a screw 34 to the lens board 20. The levers 17 are connected by a bridge 21 carrying a cam follwer 22 engaging a cam 23 on a shaft 24 geared to the hand wheel shaft in such manner that the cam makes one revolution during the traverse of the head from the minimum to the maximum enlarging positions. The gear shaft 26 carries a sprocket 37 engaging the chain 15. Movement of the head moves the lens board on the guides 28 to maintain correct focus. A set of cams is provided, one for each lens, and the appropriate cam is mounted on shaft 24, located by a key, and is fixed by a thumb nut 29. The set of cams may alternatively be fixed on a common hub and the roller 22 shifted. The position of the cross-bar 19 is adjustable along links 18 into holes 30 to avoid the use of very large diameter cams for very short focus lenses. The column may swing round to permit the lens to focus on the floor, manual focusing being effected by screw 34, an indicator 35 being provided to permit re-setting for automatic focusing. The manual focusing permits of obtaining out-of-focus effects and also for correcting for the thickness of the negative. A bracket may be provided on the lens board to take an exposure meter.