Lens aperture structure for diminishing focal aberrations in an electron gun

A main lens of an electron gun of a cathode ray tube, the main lens for receiving three parallel electron beams from the electron gun, the lens focusing each electron beam along a corresponding focal axis incident to a display surface, comprising:

• a first grid electrode positioned substantially orthogonally with respect to the three electron beams, the grid electrode including three apertures, each aperture corresponding to a respective one of said three electron beams and being substantially aligned therewith, each aperture being centered about a respective one of said focal axes and having a shape expressed by the equation (1):
• ( x a ) 2 n + ( y b ) 2 n = 1 ( 1 )
• where x and y define respective horizontal and vertical axis locations in the Cartesian coordinate system
• where a and b define respective horizontal and vertical axis half-widths of the aperture and the exponent n determines the deviance of the aperture from ellipticity, where 1<n<2
• wherein differential values of n are used for each aperture so that the shape of each aperture reduces main lens focal aberrations for its corresponding electron beam.

A color cathode ray tube, comprising:

• an electron gun for providing three parallel and co-planar electron beams to a display surface of the color cathode ray tube;
• a first electrode lens for receiving three parallel and co-planar electron beams from the electron gun, the lens focusing each electron beam along a corresponding focal axis incident to the display surface and being positioned substantially orthogonally with respect to the three electron beams, the electrode lens including three apertures, each aperture corresponding to a respective one of said three electron beams and substantially aligned therewith, each aperture being centered about a respective one of said focal axes and having a shape expressed by the equation (1):
• ( x a ) 2 n + ( y b ) 2 n = 1 ( 1 )
• where x and y define respective horizontal and vertical axis locations in the Cartesian coordinate system
• where a and b define the horizontal and vertical axis half-widths and the exponent n determines the deviance from ellipticity, where 1<n<2;
• a second electrode lens between the first electrode lens and the display surface so as to be substantially orthogonal with respect to the focal axes, the second electrode lens including three further apertures, each further aperture corresponding to a respective one of the three apertures of the first grid electrode and being substantially aligned therewith,
• whereby the shape of the plurality of apertures diminishes focal aberrations of the lens.