Patent GB-1118059-A (GB)
Title: Optical viewing apparatus
IPC: H04N5/74
Filed: 1966-11-14
Abstract: 1,118,059. Light modulators. ERNST LEITZ G.m.b.H. 14 Nov., 1966 [16 Nov., 1965], No. 50857/66. Heading H4F. In an optical viewing apparatus in which an electrostatic image converter 3, Fig. 1, comprises a photo-conductive layer 2 spaced from a deformable transparent synthetic plastics material layer 7, layers 2 and 7 being carried on glass plates 4 and 8 with transparent electrically conductive layers 5 and 9 across which a voltage is applied, deformation of layer 7 is caused when an objective 1 forms an image of a remote object on photo-conductive layer 2, and the light from a source 13 is modulated in accordance with the deformations by means of a Schlieren optical projection system including gratings 23 and 24 to form a projected image of the remote object on surface 22. The brightness of the projected image is controlled by alteration of the voltage of the D.C. source 10 by means of voltage regulator 12 controlled by a photo-sensitive element 11 which is responsive to the brightness of the projected image. A mirror 26 rotatable through 360 degrees is arranged to reflect light into the objective 1 and is coupled by a gearing having a transmission ratio of 2 : 1 to a deflector prism 27 in the path of the light rays incident on the projection surface. Two image converters each comprising a photo-conductive layer, one being responsive to the visible region of the spectrum and the other to the infra-red region of the spectrum e.g. PbS or Sb 2 S 3 , may be alternatively moved into an operative position by means of a motor for day and night use. Means responsive to the brightness of the projected image or of the field of view of the apparatus may be arranged to initiate automatic replacement of the visible region converter by the infra-red region converter and the switching on of an infra-red searchlight when the brightness falls below a minimum value. Instead of mirror 26, objective 1 may be arranged to pivot for altering the field of view. Objective 1 may comprise a pancratic lens and together with a projection objective of the Schlieren arrangement may be arranged to form a panoramic image. To improve the image quality plate 4 may be provided with a vacuum deposited screen or grating, or the objective may be provided with means for forming an intermediate image, a grating being arranged to oscillate in the intermediate image plane at a frequency which is sufficiently high to maintain the deformation of the deformable layer. Since the light from lens 15 is incident at an angle on to the deformable layer 7, correcting means such as cylindrical optical systems may be provided in the light path between layer 7 and surface 22. For colour projection a disc having three different colour filters is rotated between objective (1) and converter (3), Figs. 3, 3a and 3b, not shown, and a similarly constructed second disc rotating in synchronism with the first disc is disposed in the path of the light rays to the projection surface. The filters in the second discs are preferably corrected in accordance with the spectrum of light source 13. An infra-red image may be converted into a coloured visible image by providing three different graded infra-red filters in the first disc instead of blue, green and red filters, Fig. 4, not shown.