An electrostatic image tube with plane windows at input and output

Most modern image converters with electrostatic focus are based on the electron of concentric spheres, which was analyzed by Schagen et al, in 1952. Tubes of this type yield sharp images of good brightness with a very simple point-symmetric diode structure. One disadvantage of this type of optics is its need for an input surface of spherically-convex shape. This feature complicates the adaptation of image tubes to optical systems and may also require the use of separate lenses for field flattening.