Focal properties and chromatic and spherical aberrations of the three-electrode electron lens

Abstract

Published theoretical and experimental values of the focal lengths of simple three-electrode electron lenses are compared and found to be in general agreement. These are presented in the form of graphs which show directly the dependence of focal length on lens geometry and voltage ratio. Analogous graphs are derived for spherical and chromatic aberrations in the form of the ratios CS/S and CC/S (S being the separation of adjacent electrodes), and the general relation between the various curves is discussed.