Cathode-ray tube having an electron gun with an improved main focus lens

A cathode-ray tube having an electron gun having a main focusing lens, the electron gun comprising a focusing electrode and an acceleration electrode aligned along the mean axis of emission of the electron gun, each electrode comprising:

• a plate furnished with a central hole and two outer holes, the three holes of each plate being aligned along an axis parallel to the horizontal axis;
• and,
• a portion having an inner edge that defines a single aperture elongated along the horizontal axis through which all electron beam pass;
• wherein
• the three holes are diaposed in proximity to the single aperture and are parallel to the single aperture, and
• the single aperture comprises a rectangular central portion whose larger dimension is along the horizontal axis and end portions terminating in two identical semi-ellipses of order n that are symmetric with respect to the axis of the gun, and of formula:
• (
• x
• a
• )
• 2
• n
• +
• (
• y
• b
• )
• 2
• n
• =
• 1
• in which x=a cosnθ;
• y=b sinnθ,
• the parameter n has a value different from 1,
• a is half the width of the ellipses of order n along the horizontal axis and b being half the height of the ellipses of order n along the vertical axis,
• x represents the abscissa of a point lying on the ellipse of order n and y is the ordinate of a point lying on the ellipses of order n,
• θ is an angle which varies in one quadrant between 0° and 90°.