| 摘要 |
PURPOSE:To correct an angle and a quantity independently by preparing a memory means, in which the value of sintheta and the value of costheta are stored respectively to each correction angle theta of astigmatism correction in a quadripole electromagnetic lens system, and reading out those values for processing. CONSTITUTION:A device provided with the first and second quadripole electromagnetic lenses P1-P4 and Q1-Q4 arranged at an angular separation of 45 deg. is provided in order to correct the secondary astigmatism of an electron microscope or the like. And a correction angle theta set by a potentiometer 17 is supplied to the first and the second ROM19 and 20, in which the values of sintheta and costheta corresponding to each value of theta are memorized, through an AD converter 18, followed by reading them out to control the exciting coils 5 and 6 of the electromagnetic lenses through the DA inverter 21 and 22 as well as the constant- current circuits 7 and 8. Further, the reference of the DA inverters 21 and 22 is changed by the potentiometer 25 in order to control current quantity. Accordingly, the angle and the quantity can be independently controlled thus improving feasibility of operation. |
