Shadow mask for cathode ray tube (CRT)

A Cathode Ray Tube (CRT), comprising:

• a panel having a phosphor film arranged on an inner surface thereof;
• a funnel connected to the panel;
• a neck connected to the funnel;
• an electron gun contained within the neck and adapted to emit electron beams;
• a deflection yoke arranged around an outer circumference of the funnel to deflect the electron beams emitted by the electron gun;
• and
• a shadow mask arranged within the panel to color-selectively pass the electron beams emitted by the electron gun;
• wherein the shadow mask includes an effective screen portion having a plurality of beam passage holes arranged in a predetermined pattern, and a non-holed portion surrounding the effective screen portion and having no beam passage holes;
• wherein the beam passage hole has a large-sized hole portion on a side facing the panel, and a small-sized hole portion that is smaller than the large-sized hole portion on a side facing the electron gun;
• wherein a concave portion having the shape of a circular arc is arranged on each of the beam passage holes in a direction from a center of the effective screen portion to a direction of emission;
• wherein the concave portion is varied from the center of the effective screen portion diagonally such that a serif width D of the concave portion satisfies D=a−bx+cx2 (wherein a, b, and c are dimension less constants, and x is a spatial distance from the center of the effective screen portion to a center of the beam passage hole) both x and D being distances;
• and a, b, and c selected such that {c/(b+c)}has an absolute value between 0.0092 and 0.0099.