| 摘要 |
PURPOSE:To correct the astigmation produced from a low potential electrode through a high potential electrode, by setting such that the distance between the centers and the horizontal and vertical holes in a pair of electrodes for forming a main electronic lens are arranged in a specific relation to each other. CONSTITUTION:In a pair of electrodes for forming a main electronic lens, the hole diameter b1 in the direction of Y-Y' axis of a low potential side electrode, third grid 40 is made larger than the distance between the centers of each electron beam pass hole sections 42-44 while S1 and the hole diameter a1 in the direction of X-X' axis are made approximately equal and b1/a1 is made larger than 1.06. The hole diameter b2 in the direction of Y2-Y2' axis of a high potential side electrode or fourth grid 50 is made larger than the distance S2 between the centers of beam pass hole sections 52-54, while S2 and the hole diameter a2 in the direction of X2-X2' axis are made approximately equal, and b2/a2 is made more than 2% larger than b1/a1. Consequently, the astigmation produced through noncircular beam pass hole section of low potential side electrode can be eliminated. |
