The performance of an electron lens depends solely on the size of the space between the pole pieces. This may be a simplification, but not much of one.

In this article, I will describe the operation of electron lenses in general but with specific reference to how they relate to working with SEM long working distances. The theme is related to EBSD performance when long working distances are needed with steeply tilted samples, and where large beam currents are needed to reduce noise in the EBSD pattern.

The lenses in electron microscopes are made of magnetic fields. The field bends the path of the electrons as they travel through it and so focuses them. The magnetic fields are themselves produced by an electric current flowing through a coil of wire. As the current is increased, the field gets stronger and so the lens focuses more strongly - up to a point.