An afocal electrostatic lens

Abstract

The focal properties of a pair of lenses spaced so that the second focal point of one and the first focal point of the other coincide are discussed. It is shown that if the two lenses are identical they form a system with the property of forming an image at a fixed distance from an object and with a magnification that depends only on the overall voltage ratio (as V'/V)-14/). The focal condition which the voltage ratios of each lens must satisfy is shown to be a constant separation of focal points. Calculated focal loci are presented for some equal diameter cylinder lenses.