| 摘要 |
PROBLEM TO BE SOLVED: To provide an electrostatic type astigmatism compensator where aberrations due to a higher-order component, such as a 6θcomponent and a 10θcomponent will not be produced, even when a large astigmatism compensating output is outputted. SOLUTION: In this astigmatism compensator, electrodes 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, 1I, 1J, 1K, 1L, 1M, 1N, 1O, 1P are formed in a 16 fold symmetrical form with respect to an optical axis. By defining voltages applied to respective electrodes 1A, 1B,..., 1P as VA, VB,..., VP, respectively, voltages Vx, Vy are applied from two power sources, so as to satisfy VA:VB:VC:VD:VE:VF: VG:VH:VI:VJ:VK:VL:VM:VN:VO:VP=+Vx:+(Vx+Vy)/21/2:+ Vy:-(Vx-Vy)/21/2:-Vx:-(Vx+Vy)/21/2:-Vy:+(Vx-Vy)/21/2:+Vx:+(Vx+ Vy)/21/2:+Vy:-(Vx-Vy)/21/2:-Vx:-(Vx+Vy)/21/2:-Vy:+(Vx-Vy)/21/2.
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