Abstract: A computational investigation has been carried out in the field of non-relativistic charged-particle optics using the charge density method as a boundary value problem with the aid of a personal computer under the absence of space-charge effects. This research has been concentrated on designing a non-equidiameter electrostatic immersion lens whose electrodes are cylindrical in shape separated by an air gap. The variable parameter of the 2 electrodes is the applied voltage ratio. The axial potential distribution of an electrostatic immersion lens has been computed by taking into consideration the distribution of the charge density due to the voltages applied on the 2 cylindrical electrodes. Potentials have been determined anywhere in space by using Coulomb?s law. The optical properties of the immersion lens have been investigated under finite and zero magnification conditions.