Answers are grounded in this paper and cite their sources.
Power series are derived with which, given data on the electric field, the focal properties of some common electron lenses can be quickly computed even when the speed of the electrons approaches that of light. The expansion is in powers of the ratio of the P.D. across the lens to the sum of the P.D.'s between its electrodes and the cathode (for electrons) or anode (for positive ions), squares of this ratio being neglected in comparison with unity. As an example the focusing properties of two cylinders almost in contact are calculated.
No takes yet. Share an insight, caveat, or question.
Hansen et al. (1936) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: