Cathode-ray tube having an astigmatic lens element in its electron gun

Claim 1

A cathode ray tube for color television, comprising: a. an evacuated envelope having a window at one end thereof; b. a screen disposed at said window and comprising electronresponsive luminescent areas emitting light of various colors; c. means for scanning an electron beam across said luminescent screen in the direction from a first side thereof toward an opposite side; d. electron gun means within said envelope for producing an electron beam, said electron gun comprising a cathode and at least a first, second, and third grids, said first and second grids respectively controlling and accelerating said electron beam, said second grid having a surface portion facing said first grid and said third grid having a first surface portion remote from said cathode and facing toward said luminescent screen, said electron gun further comprising plate means comprising an astigmatic lens element located between said surface portion of said second grid and said first surface portion of said third grid, said astigmatic lens element being a rotationally non-symmetric passage through which said electron beam passes and which has two main axes which are orthogonal with respect to each other and with respect to the axis of said electron gun, the dimension of said passage along one of said main axes significantly exceeding that along the other said axis and said one axis being substantially parallel to said scanning direction of said electron beam; and e. a shadow mask having a plurality of apertures extending therethrough located between said luminescent screen and said electron gun, and having said apertures disposed at said electron-responsive areas that are accessible to said electron beam via said apertures, said shadow mask being substantially parallel to and proximate with said luminescent screen, whereby there is a reduced incidence of visible moire fringes resulting from interference between a pattern of lines on said luminescent screen scanned by said electron beam and a pattern of said apertures arranged along lines on said color selection electrode.