A 'movable' electrostatic lens

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Abstract
A novel electrostatic lens system consisting of several short, closely-spaced elements is described. By applying the appropriate voltages to these elements it is possible to simulate a lens having longer elements and a variable position. If such a lens has n independent voltages it can be used to maintain (n-1) properties of an image, or of more than one image, constant while other properties are varied, within the constraints imposed by the Helmholtz-Lagrange relationship. The properties are the position, energy, linear magnification and angular magnification. A movable three-cylinder lens is considered as an example and the necessary data are presented to enable three different pairs of image properties to be kept constant. It is shown that the lens can be operated over wide ranges of the variable image properties.

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