Patent ID: 7459840

Claim:
A shadow mask for a Cathode Ray Tube (CRT), comprising: an effective screen portion including a plurality of beam passage holes arranged in a predetermined pattern; and a non-holed portion surrounding the effective screen portion, the non-holed portion including no beam passage holes; wherein the beam passage holes have a large-sized hole portion on a side facing a panel of the CRT, and a small-sized hole portion that is smaller than the large-sized hole portion on a side facing an electron gun of the CRT; wherein a concave portion 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 of the electron gun of the CRT; 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+cx 2 (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 D and x being distances; and wherein a, b, and c are selected such that {c/(b+c)} has an absolute value between 0.0092 and 0.0099.