Patent GB-394385-A (GB)
Title: Improvements in optical systems for the projection of erected images
IPC: G02B27/14
Filed: 1931-12-24
Abstract: 394,385. Optical systems ; colour kinematography. HILGER, Ltd., A. and DOWELL, J. H., 98, King's Road, Camden Town, London. Dec. 24, 1931, No. 35746. [Class 97 (i).] In a system comprising reflectors for projecting and erecting companion images, particularly for projecting kinematograph pictures in colour from films having the component images arranged side by side with their widths along the length of the film, registration is effected by movement of one of the reflecting surfaces or of a group of them, and the rays from the companion images are completely separated before registration by reflecting surfaces so displaced out of co-planar setting that a dividing screen can be brought right up to the point where the optical paths of the beams diverge from one another. Figs. 10 to 12 show one form for projecting pairs of images, in which each light beam undergoes three reflections at the cathetus faces of right-angled prisms, Fig. 10 being a plan, Fig. 11 a side view and Fig. 12 a front view. The rays from the lefthand image are incident on a prism A1 by which they are reflected down to a prism B1 reflecting them to the right on to a prism C1 by which they are reflected towards the projection screen. The rays from the righthand image are reflected upwardly by the prism A2, then to the left by the prism B2 and then forwardly by the prism C2. The prism C2 is separate from the others and is adjustable about two axes at right-angles to register the projected images on the screen ; the other five prisms are all cemented together. Interference between the two images is prevented by extending the dividing screen S so that it passes between the prisms A1, A2. The displacement of the two beams produced by this system are symmetrical in relation to the axis of the projector and are small enough to allow the light to pass through an ordinary projection window. A mounting for this system is described. Figs. 13 to 15 are views similar to Figs. 10 to 12 of another system in which each beam undergoes four reflections so that the system can be used for the projection of film taken by a camera operating on its side and not fitted with an erecting device, the film being used in the projector the normal way round, i.e. emulsion side towards the condenser. This system comprises two units, one for each image, each comprising three right-angled prisms A1, B1, C1 and A2, B2, C2. Each prism B1, B2 is arranged so that its cathetus face serves as a light entrance and exit surface and the light is reflected by each of the other two faces. Light from the left-hand image enters the prism A1 and is reflected down into the prism B1, the roof edge of which is below the cathetus face and inclined at 45‹ to the axis of the lens system. After two reflections by the prism B1 the light enters the prism C1 by which it is reflected towards the screen. Light from the right-hand image undergoes similar reflections by the prisms A2, B2, C2. With this sytem the emergent rays are in the same horizontal plane as the incident rays. Registration is obtained by making the unit A1, B1, C1 adjustable, the adjustment indicated in Figs. 13 and 14 being about two axes at right-angles intersecting at the point F. The screen S extends between the prisms A1, A2.