Patent GB-1198655-A (GB)
Title: Entrant Beam Optical Scanner.
IPC: H04N1/06
Filed: 1967-06-19
Abstract: 1,198,655. Optical recording and playback. AMPEX Ltd. 19 June, 1967 [20 June, 1966], No. 28235/67. Heading G5R. [Also in Divisions G2 and H4] A collimated beam of light 15, originating, for example, from a laser, is reflected as a beam 58 from a rotating polygon 38 and impinges on a stationary reflector 51 having its centre of curvature coincident with the axis of rotation of polygon 38. The beam is returned as a beam 56 to the axis of rotation where it may enter a lens 40 having its nodal centre located on the axis of rotation. A focused light spot is thereby formed which scans over a circular arc as the polygon rotates. The arrangement is used in conjunction with a photographic film or printed material 12 which is curved in coincidence with the scan path and is moved in a direction at right-angles thereto. For recording pictorial or other information on the film, the light beam 15 is modulated in response to electrical signals representing the information. To read out information from the film, the beam is left unmodulated and a photo-multidlier tube is located on the opposite side of the film to that which is scanned. Reflector 51 is a spherical reflector and functions in conjunction with a spherical and concentric refractor 52 which is provided with a strip reflector 54 on the surface facing reflector 51. The refractor is located so that reflector strip 54 is at the focus of reflector 51, the arrangement functioning as a reflex catadioptric system in which the beam enters through refractor 52, is focused by reflector 51 on reflector strip 54, then returns to reflector 51 and finally passed through the refractor 52 to emerge as collimated beam 56. Lens 40, which is described more fully with reference to Figs. 4 and 5 (not shown), consists of an inner part sphere to which are cemented two annular part hemispheres, all optical surfaces of the elements being concentric as well as spherical. A beam-splitter system, Fig. 7 (not shown), may provide one or more further input light beams, such as beam 59, which comes into operation in sequence as polygon 38 rotates whereby the rotation speed may be reduced for a given scan speed. A servo system is provided to relate the scanning speed with the speed of movement of the film. In a first modification, Fig. 8 (not shown), a rotating 45 degree pyramid replaces polygon 38 and a 45 degree plane reflector is included to change the directions of the input and output light paths. A second modification, Fig. 9 (not shown), also utilizes a rotating 45 degree hexagonal pyramid but dispenses with lens 40 and locates the film at the focus of reflector 51, i.e. at the position of reflective strip 54 in Fig. 6. In this arrangement the film is curved to present a convex surface to the scanning beam. A correcting refractor is included in the incident light beam to reflector 51 and forms a catadioptric system therewith. The input collimated beam 15 is also expanded in diameter by a lens system and passed through a filter to correct the intensity distribution. A third modification, Fig. 3 (not shown), utilizes a catadioptric system formed of reflector 51 and an incident beam refractor and may have the film located either at the focus of the reflector or at a displaced position, as in Fig. 6, where the beam is focused by a lens 40. This modification uses a rotating polygon beam scanner. A third modification, Fig. 2 (not shown), uses a cylindrical reflector.