The magnification behaviour of a five-element electrostatic lens

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Abstract
The authors have made an experimental study of a five-element afocal lens and find that the magnification, M, depends on the overall voltage ratio, V5/V1, in exactly the manner predicted earlier, i.e. M=(V5/V1)-14/. For lenses of different proportions they find that the prediction of a simple scaling law for the focusing potentials is valid. They have extended their measurements to five-element lenses with potential distributions different from those used in the afocal lens and have demonstrated 'true zoom' action in which the magnification can be varied over a range of some 9:1 at a given overall voltage ratio. Measurements made over a wide range of focusing potentials show that the five-element lens could be operated to give constant magnification over an extremely wide range (104:1) of overall voltage ratio or to give constant angular magnification over a smaller, but still substantial range (100:1). The authors present design curves from which the potential distribution required for a specific purpose can be simply obtained.

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