Electrostatic lenses were essentially the first types of electron lenses to be employed in an electron optical system. The electrostatic unipotential electron lens is the most useful for incorporation into a general electron or ion optical system since it is essentially analogous in function to a single converging glass lens in a light-optical system. The beam-forming system of any electron or ion optical system employs, to a certain degree, some basic features of the cathode lens. Ion optical systems can be conceptually identical to many electron optical systems, with electrostatic lenses replacing magnetic lenses. Static lens is an axial short-focus lens just as the electromagnetic lens is an axial short-focus lens, that is, it can accomplish linear ion beam focus along the optic axis of the ion optical system. The electron optical systems are mostly characterized by small aperture angles leads to a decisive advantage where image focus is concerned.