Spherical Aberration of Compound Magnetic Lenses

摘要

A reduction of the spherical aberration of strong electron lenses can be achieved by a strong lens as a virtual image former and by a transformation of the image in a real one by means of one or more weak lenses. Calculations are carried out for bell-shaped magnetic fields of the axial field distribution H(z)= H0 1+(z/a)2 , and numerical values of the achieved reduction of the aberration are given for different lens strength, magnification, and image distance of the compound system.