1. Crewe AV, Kopf D (1980) A sextupole system for the correction of spherical aberration. Optik 55:1–10
2. El-Kareh AB, El-Kareh JCJ (1970) Electron beams, lenses, and optics. Orlando Academic Press, Orlando
3. Glaser W (1956) Elektronen- und Ionenoptik. Handbuch der physik 33:123–395
4. Glaser W, Lammel E (1943) Arch Elektrotech 37:347–356
5. Grivet P (1972) Electron optics: translated by PW Hawkes, revised by A Septier (2nd English edn). Oxford Pergamon Press, Oxford