Key points are not available for this paper at this time.
A least-squares collocation method has been used to calculate the potential distributions of electrostatic immersion lenses consisting of three thin coaxial apertures at three different potentials. The focal lengths, principal plane positions and spherical aberration coefficients have been obtained by numerical integration of the ray equations for a wide range of values of the aperture potentials and for various aperture diameters and spacings. The use of these lenses as zoom lenses is discussed.
F H Read (Sun,) studied this question.