GB886413A - Improvements in or relating to deflection and focusing apparatus for cathode ray tubes - Google Patents

Abstract

886,413. Cathode-ray tubes. MULLARD Ltd. March 4, 1958 [Dec. 23, 1957], No. 32966/61. Divided out of 886,412. Class 39(1) A cathode-ray tube scan magnification and beam focusing system includes a magnifying immersion lens L3, Fig. 1, of such strength as to over-converge the beam in both the deflection and orthogonal planes, thereby magnifying the scan in each of these planes in a negative sense, and a focusing lens which may be as indicated, a pair of quadripole lenses L1, L2 orientated mutually in quadrature, or a spherical lens. The magnifying lens L3 has one or more internal foci and is, preferably, a spherical lens with two internal foci magnification is in a positive sense. The spherical focusing lens if used may also have one or more internal foci. The effective deflection centre of the deflection means in each plane is located between the effective centres of the focusing and magnifying lenses and both deflection centres preferably coincide. Fig. 2 shows a quadripole lens structure having a square permeable core with four pole-pieces each of which. has a pole face of rectangular hyperbolic form and with D.C. fed energizing windings. In Fig. 4 a line and frame scanning deflection coil system 60 is located between electromagnetic focusing and magnifying lenses Lf, Lm. A deflection system may be used in which the beam is deflected first in one direction and then in the opposite direction so as to cross the optical axis. The invention is described with reference to raster scanning applications e.g. in television, oscilloscope or storage tubes, but reference is also made to uni-dimensional line scanning applications. Specifications 827,851 and 846,544 also are referred to.