GB451766A - Improvements in or relating to cathode ray tubes - Google Patents

Abstract

451,766. Cathode-ray tubes; photoelectric cells. BROADWAY, L. F., Strathmore, Park Way, Hillingdon, Middlesex. Nov. 8, 1934, No. 32181. [Class 39 (i)] An electrostatic electron lens comprises two apertured electrodes between which a focusing field is maintained, and in at least one electrode, the surface bounding the part of the aperture facing the co-operating electrode is so shaped that at any point in this part the field component perpendicular to the axis is proportional to the distance from the axis. This is stated to give perfect focusing. It is shown mathematically that in the absence of disturbing fields axial sections of the surface are hyperbolas, having an angle of 70‹ 321 between the asymptotes. Fig. 8 shows a lens system constituted by electrodes 6, 7 of hyperbolic section, together with a remote first anode 8 having a diaphragm 21 and a cathode 4 and shield 5 of hyperboloidal or frusto-conical shape. A single electrode 9, Fig. 5, may consist of diaphragms 11, 12 constituted by conical frusta having semi-vertical angles 54‹ 44<1>, or the surfaces 11, 12 may be rounded to approximate hyperboloids. In modifications, annular diaphragms, the inner edges of which lie on a hyperboloid, may be mounted in a cylinder or two curved conical frusta may lie one at each side of a central diaphragm or two conical frusta may be joined by a cylindrical member having a central diaphragm. The invention is applicable to devices in which electrons from a photo-electric surface are focused onto a mosaic screen. Lenses analogous to optical cylindrical lenses may be constructed. Specification 431,327 is referred to.