| 摘要 |
PROBLEM TO BE SOLVED: To accurately measure even if measuring positions are slightly varied, when displaying an image band along the long sides of the upper and lower ends of an image plane and inspecting the upper and lower pin cushion distortions and horizontal trapezoidal distortions of the image plane, by slanting the long side in the vicinity of a diagonal part of an effective surface of a shadow mask along the bow-like arrangement of electron beam passing holes. SOLUTION: Preferably in this color picture tube, at least 10 mm of the long side in the vicinity of a diagonal part of an effective surface is slanted. Since the vertical deviation of the electron beam 16 entering the effective area of a phosphor screen 2 is small, distortions can be measured accurately in the vicinity of the short axis end of the image plane by being hardly affected by a step 4, even if the position of a CCD camera are varied slightly. Since the long side in the vicinity of the diagonal part of the effective surface of the shadow mask is slanted along the bow-like arrangement of electron beam passing holes 16 in the vicinity of the diagonal part of the long side, the measurement accuracy of the distortions is not varied, even if they are measured at one end side of the step 4 or at the other end side thereof, so that they can be measured accurately in the vicinity of the diagonal part of the long side of the image plane.
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