Patent GB-1051065-A (GB)
IPC: G02B27/14
Abstract: 1,051,065. Optical apparatus. ELECTRIC & MUSICAL INDUSTRIES Ltd. July 15, 1963 [July 14, 1962; Aug.11, 1962; Sept.21, 1962; Nov.9, 1962; May 16, 1963], Nos. 27150/62, 30877/62, 35944/62, 42516/62 and 19423/63. Heading G2J. [Also in Division H4] A colour television camera, Figs. 2 and 3, comprises a luminance pick-up tube 4 one or more colour pick-up tubes 5 and an optical system 3 for applying image light to the tubes the system being such that an optical image of greater depth of focus is formed on the target of the luminance tube than on the target of the/or each colour tube. Thus in Fig. 2 a small mirror deflects incoming light from only a small axial zone to tube 4, allowing light from the marginal zones to pass to tube 5, whilst in Fig. 3 a similar result is obtained by allowing light to pass to tube 4 via a small aperture in a mirror. In a typical arrangement the small mirror or aperture may be of such a size as to define an effective aperture of f 8 for tube 4, so as to provide a suitable depth of focus, whereas the camera objective 2 may have an aperture of # 4 whereby the image formed on tube 5 is of smaller depth of focus. The invention permits the camera to make greater use of the available light since the objective does not have to be limited to an aperture which provides an appropriate depth of focus for the luminance tube. The reduced depth of focus for the colour tube or tubes is tolerable since they are only required to generate low definition signals. The Specification discloses more detailed arrangement based on Figs. 2 and 3 with reference to Figs.4, 6, 7, 8, 9 and 15 (not shown) and see Fig. 13 in which provision is made for the use of zoom tubes, lens turrets, relay lenses, folded optical systems, camera tubes of different types and sizes and numerous other optical features. Fig. 13 illustrates a typical arrangement where the camera incorporates a zoom lens 35 which forms a real image at the position shown dotted which is then transferred to three vidicon colour tubes 32-34 by way of transfer lens 36, dichroic mirrors, 41, 42, reflecting mirrors 39-41 and objective lenses 43-45. A small mirror 37 (corresponding to mirror 3 in Fig. 2) diverts the axial light to the luminance tube 31 (an image orthicon) by way of reflecting mirror 38. Fig. 13 also incorporates electrical means for varying the effective depth of focus of the luminance signal channel without actual aperture adjustment of the camera. The luminance signal from tube 31 appears across potentiometer 75 whilst a second low definition (small depth of focus) signal is produced across a potentiometer 78 by matrixing the outputs of tubes 32-34 in circuit 74. The two potentiometers are gauged for inverse operation and the luminance signal output terminal 77 is coupled to the potentiometer sliders via resistors 76 and 79. A modification, Fig. 14 (not shown), involves only a simple potentiometer connected between the two luminance signal sources 31,and 74. The low definition luminance signal may be derived from a second luminance tube. A camera according to another aspect of the invention is illustrated in Fig. 5 where light from a lens 23 is directed to a luminance tube 10 and two colour tubes 11 and 12 by way of dichroic mirrors 13, 15 and reflecting mirrors 14, 16. The tubes have individual objective lenses 17-19 with iris diaphragms 20-22 which may be adjusted so that diaphragm 20 has the smallest aperture and thus provides an image for luminance tube 10 of greater depth of focus than those provided for colour tubes 11 and 12. Reference is made to the use of a five-tube camera in which four tubes operate in accordance with the invention to provide signals at one scanning standard, e. g. 405 lines and the fifth tube function to provide a monochrome signal at a second scanning standards, e.g. 625. Where a single colour tube is used this may operate in conjunction with a colour selection filter formed of a plurality of differently coloured vertical strips. Fig. 10 illustrates a detailed optical system for use in the invention and arranged so that mirror 53 (which corresponds to mirror 3 in Fig.2) is located in the path of parallel rays. Lens 51, which may be a zoom lens or other complex lens, tends to focus image light at point A but a concave lens 52 located at a distance from A equal to its focal length diverges the light into parallel rays. The axial rays deflected by mirror 53 are focussed on the luminance tube at C by objection 55 whilst the remaining marginal rays are focussed in the colour seetion of the camera at B by objection 54. Figs. 11 and 12 illustrate optical systems equivalent to those shown in Figs. 3 and 2 respectively which are formed of pairs of prisms 62, 63 separated by an air space except where they are jointed by a transparent substance 64 e.g. Canada Balsam. The lower face of prism 63 is blackened at 66 to prevent the reflection of unwanted light.