Patent GB-822166-A (GB)
Title: Cathode ray image producing system and apparatus
Inventor: FRIES GUSTAV
IPC: H01J31/50
Filed: 1954-09-20
Abstract: 822,166. Cathode-ray tubes. VREDENBURG-INGLESBY, J. C. Sept. 20, 1955 [Sept. 20, 1954 ; Feb. 14, 1955], Nos. 27186/54 and 4300/55. Class 39(1). [Also in Groups XX, XXXV and XL(b)] An image producing system comprises a photocathode and a fluorescent or other image display target on a common axis facing one another and one or more focusing magnets for producing an axial field (i.e. directed along the common axis) and arranged entirely beyond the part of the axis confined between the photocathode and target so that the focusing effect of the magnetic field causes an enlarged or reduced image on the display target according as to whether the magnet or magnets are arranged adjacent the photocathode or display target respectively. It is stated that the incident light on the photocathode may be replaced by ions or neutrons. The magnetic means may be a coil 5 energising magnetic core 6<SP>1</SP> or a permanent magnet e.g. by making all or part of the core a permanent magnet. In one form Fig. 1 a continuously evacuated or sealed off tube comprises a fluorescent screen 2 an aluminium cathode 1 and an anode 4 at 5000 volts positive to the cathode and coil 5 with magnetic core 6<SP>1</SP> is placed at the cathode end of the tube. The pressure is 10-<SP>3</SP> mm Hg. so that the discharge when started just fails to extinguish and a blurred enlarged image of the cathode appears on the fluorescent screen. The sharpness of the image is adjustable by moving the coil backwards or forwards, by moving the core 6 only or by adjusting the current flow in the coil by variable resistance 10, without it is stated altering the degree of enlargement of the image. The magnetic core may be solid, Fig. 2 (not shown), and a disc of greater diameter than the core can be mounted on the end of the core to reduce the degree of enlargement of the image. Yoke legs or a cylindrical yoke may be attached to the core at one end and extend around the coil 5. To obtain greater image enlargement (magnification) the core diameter is reduced and the core is preferably tapered to a point or small area at one end (the end adjacent the cathode.) Fig. 4. In this case the image of point 14<SP>1</SP> occupies the whole of the screen. By directing the point to different parts of the cathode, e.g. by tilting the core, different parts of the cathode can be shown on the screen. Focusing is achieved by moving the point towards and away from the cathode or by varying the current in coil 5. Alternatively the size of the image can be reduced to point size by fitting the coil and core at the screen end of the tube, Fig. 4 (not shown). The beam can pass out of the tube through a window and be focused on to photographic material outside the tube. In another form, Fig. 5 an optical image is projected through the hollow magnetic core 6<SP>1</SP> or from the opposite side of the tube on to photocathode 3 the electron image being accelerated by 20000 volts on anode 4 to strike fluorescent screen 2. In another form, Fig. 6, electrons are released from photocathode 3 and go to calcium tungstate fluorescent screen 2 to form an enlarged image ; the image enlargement is stated to be due mainly to the curved magnetic field lines at the end of the core which spread the electrons out into a fan shape. The core 6<SP>1</SP> is displaced axially for focusing, sharp focusing being achieved in either of two positions of the core. The cathode may be shaped as a segment of a sphere which tends to enlarge the image still further, Fig. 7 (not shown). In other forms there may be two concentric coils the outer being axially movable or having means to vary its current to correct image distortion, Fig. 8 (not shown). There may be three coils on an iron core the angle of the field lines being altered to correct distortion of the image by displacing the coils on the core or by passing different currents through the coils, Fig. 9 (not shown). The core is made up of three telescopically adjustable tubes to allow of " image distortion correction," Fig. 10 (not shown), or the core may have legs pivoting on hinges, four small permanent magnets compensating for pin cushion distortion, Figs. 11, 12 (not shown). The cathode may be square or circular, Fig. 13 (not shown), the image being distorted into a rectangular or elliptical shape. This embodiment is stated to be useful for the production of wide screen cinema pictures, reproduced directly from film or indirectly by a television system, and the system being distortion compensated by the means of Figs. 11, 12 (not shown). For production of large screen images of television pictures, a television projection receiver tube projects an optical image via an optical system on to the photocathode of Fig. 5, or a cinematograph film is projected on to this photocathode by a torch lamp bulb. Both television and home cinema pictures can be projected alternatively on the same screen by a suitable optical selector device. The invention can also be used to produce enlarged images from eyepieces of optical microscopes and telescopes or as an enlarger for photographic purposes. In one such form, Figs, 14, 15, a prism 33 can be turned about the axis of coil 5 to selectively reflect images from a cathode ray receiver tube, cinema projector 31 and optical microscope 32 on to semi transparent photocathode 3. The electron image impinges on large fluorescent screen 2 under control of magnetic coil 5 and core 6<SP>1</SP>. The first Provisional Specification states also that the invention can be applied to electron microscopes. The specimen can be mounted or spaced from the cathode in which case the cathode can be the tapered end of a magnet core as in Fig. 3, introduced into the vacuum chamber. If the specimen is spaced from the cathode the image of the specimen rather than the cathode is projected on to the display target.