| 摘要 |
PURPOSE:To eliminate the coma of an electron-gun structured body by providing elliptical beam-passing holes having major axes in the direction of a horizontal axis, both in an electrode of the three-pole part except the cathode and in an electrode giving a diverging action. CONSTITUTION:Electrodes 53, 55, 57 and 59 that constitute a focusing part are placed at the back of a three-pole part consisting of a cathode 47, electrodes 49 and 51. A low voltage of 500V is applied to the electrodes 51 and 55, a medium voltage of 7kV is applied to the electrodes 53 and 57, and a high voltage of 25kV is applied to the electrode 59. Elliptical beam-passing holes 71 and 67 which have major axes 72 and 69 in the direction of the horizontal axis, X, are provided in the electrode 57 side of the electrode 59 and in the electrode 49 of the three-pole part, respectively. Consequently, an asymmetric diverging action of the vicinity of the hole 71 enables the correction of the horizontal coma around the picture which is caused by barrel- like vertical magnetic field. Besides, an asymmetric focusing action of the vicinity of the hole 67 can compensate the tendency of the central part of the picture of becoming long. |
