A New Method of Astigmatic Compensation

Abstract

A new astigmatic compensator is employed in permanent magnetic excited objective (Hitachi HS - 5). The compensator is a nickel plated copper cylinder with the slitted bead. The strength of the asymmetric magnetic field in the compensator is controlled by the thickness of plated nickel.
To find quickly the compensating condition, the vector representation of the astigmatism is used. The compensating condition is. practically unchangeable even when the variaton of accelerating voltage is ±6 % at 50kV.