Patent GB-740970-A (GB)
Title: Electronic cameras for recording electron images
IPC: G03G17/00
Filed: 1953-06-10
Abstract: 740,970. Cathode-ray tubes. FRIES, G., and INGLESBY, J. C. VREDENBURG-. June 10, 1953 [June 10, 1952], No. 14581/52. Class 39 (1). [Also in Group XX] Optical images are recorded by means of an image converter tube provided with a photocathode and an oppositely-disposed electron pervious window and electrostatic and/or magnetic means for accelerating and focusing the electron image so that it passes through the window to impinge on a recording surface outside the tube, the tube and recording surface being mounted in a camera housing equipped with a lens and a shutter or equivalent means for cutting off light except during a predetermined exposure period. The images may be formed alternatively by X-rays or infra-red rays or heat images formed thereby. The recording surface is a halide film as described in Specification 715,480 or a photographic film. The electron permeable window may be a thin foil of Al, Be, cellulose acetate or mica having a thickness of 2-20Á. In one embodiment the window may be a narrow strip, and the recording surface or window is continuously moved while the electron image is swept over the window. In another form a relatively small complete electron image passes through a thicker window so that the recording surface can be stationary. In the latter case the photo-cathode is of large area and an electron optical system reduces the size of the electron image; the photographic material may be grainless collodion. In one illustrated form, Fig. 1, the device comprises camera lenses 6, image converter 2 with photo-cathode 1, accelerating and focusing electrode 3 with rear stop 4 and window 5 and glass vessel 7 sealed to the image converter by flanges and rubber ring 8. Glass vessel 7 contains fluorescent screen 12 with an aluminium film which serves as a final anode, and rectangular sectioned shoot 9 with removable cover 11 through which photographic film 10 is introduced. An annular permanent magnet 22 or electromagnet focuses the electron image on to 10 or'12. Fluorescent screen 12 is used for prefocusing of the electron image and is viewed through lens 28 having removable light-proof cover 17. Vessel 7 is evacuated to 10<SP>-5</SP> mm. in 5 minutes by a vacuum pump attached at 19, after the film 10 has been inserted. If, however, there is a second shoot at 21 and the shoots are so narrow as to fit the film, the shoots need not be sealed, but a larger vacuum pump is necessary. In a modification, Fig. 4 (not shown) using electrostatic focusing, the vessel 7 contains a conical focusing anode and an electron permeable window, a thin aluminium layer being deposited on the tube wall and window and being at the same potential as the conical anode. Image rotation when magnetic focusing is used can be compensated by rotating a prism in the objective. The photo-cathode and electrostatic lens may be in a common envelope but separated by an electron permeable foil, a window in the wall being formed by a second foil, Fig. 7 (not shown). The objective includes a totally reflecting prism and rotating mirror and a diaphragm with a narrow slot in front of the photo-cathode. The mirror is rotated in synchronism with the movement of the film by a suitable lever and cam coupling to enable the whole optical image to be recorded. Alternatively an electron image corresponding to the complete picture can be swept across window 5. In another form, Fig. 5 (not shown), an electrostatic lens reduces the size of an electron image corresponding to a complete optical image, so that the whole image can simultaneously pass out of the window. The tube voltages are supplied by condensers, by a Van de Graff generator, or through transformers and rectifiers from the mains. The window is cemented to the final anode which forms part of the tube envelope. The box surrounding the tube may fit into the lens mount of an ordinary camera and is provided at its front with a similar mount into which the camera lens fits. The image may be enlarged by adjustment of the electron-optical focusing means. In another form, Fig. 9, the tube is carried on a support 69 movable between limit stops 84, 86 about pivot 68. To take an exposure button 72 is depressed which first opens shutter 76, 77 through a linkage (not shown) and then raises the left-hand side of spring-loaded lever 81 to let support 69 and the tube move over to limit stop 86 under the action of spring 85. The film which has perforations engaging teeth on sprocket 70 is held stationary by a pawl on the sprocket. After exposure the support is returned to engage stop 84 by knob 94, teeth 96 engage a pawl controlled pinion on sprocket 70 to move the film 71 by one picture frame, and the exposed film is wound up by a knob on the spool 74 or automatically by coupling spool 74 by gearing to the pinion on the sprocket 70. 66 is an interchangeable camera lens and 78 a correcting lens and the tube end wall and photo-cathode are spherically shaped. Voltages for the tube are supplied through bearings 68. The image may be distorted, e.g. for trick photography, or corrected, by variation of the magnetic or electric focusing fields. Colour records can be obtained by recording filtered component images which can then be reproduced by projecting them through filters or printing them photographically through filters. The device may also be used in reproduction printing, colour printing " without touching-up," and photo-compositing machines. In another embodiment, an electron permeable gas-tight layer may be applied directly to the photo-cathode. Specification 715,485 also is referred to. The Provisional Specification refers in addition to forms in which an electron image originates from cathodes other than photo-cathodes, or in which protons, ions or " corpuscular radiation " is used. The photo-cathode may be of semiconducting material such as bismuth selenide or lead sulphide. The record member may be inside the tube wall or may pass through the wall.