Lens aperture structure for diminishing focal aberrations in an electron gun

A main lens of an electron gun of a cathode ray tube is provided. The main lens for receives a plurality of parallel and co-planar electron beams emitted by the electron gun. The lens focuses each electron beam along a respective one of a plurality of focal axes incident to a display surface. A first grid electrode is positioned substantially orthogonally with respect to the plurality of electron beams, the grid electrode includes a plurality of apertures. Each aperture focuses a respective one of the plurality of electron beams, each aperture is centered about a respective one of said focal axes and has a shape expressed by the equation (1):where a and b define the horizontal and vertical axis lengths, theta is an angle, which varies between 0° and 360°, with respect to the x axis, of a line between the origin (x=0, y=0) and a point on the edge of the aperture and the exponent n determines the deviance from ellipticity, and where 1