A Possible Chromatic Correction System for Electron Lenses

It is shown that a suitably arranged group of four electrodes has properties which make it a useful integral part of a system for the correction of axial chromatic aberration. Its application to the correction system proposed by Scherzer, and to a new simplified system having certain advantages over that of Scherzer is discussed. Curves are given for the chromatic and focal properties of the corrective electrode group, and an example of a corrective system is considered numerically. The effect of this system on off-axial chromatic aberration is investigated, and the possibility of combining it with a system for spherical correction is envisaged.