Shadow mask each aperture of which is defined by a quadrupolar lens

Claim 1

A color television image producing tube comprising, an evacuated envelope, means to generate a plurality of electron beams, a display screen having a plurality of regions of elongate form luminescing in different colors, means for selectively impinging said beams each upon a respective luminescent color region, said means comprising an apertured electrode system interposed between said beam generating means and said display screen, said apertured electrode system comprising a plurality of quadrupolar lenses each defining an aperture for the passage of said beams to an associated color region of said screen, said quadrupolar lens comprising two pairs of electrode elements arranged in space quadrature, the electrode elements of each pair being arranged in spaced opposing relationship transverse to the path of said beams through the aperture oppositely confronting electrodes of said pairs operating at the same potential and adjacently positioned electrodes of said pairs operating at a potential difference whereby electrostatic fields having substantially hyperbolic configurations are formed between each adjacent pair of said electrodes.