The Symmetrical Magnetic Electron Microscope Objective Lens with Lowest Spherical Aberration

Using results recently published it is shown that each of the investigated symmetrical magnetic lenses has an optimum value of the lens excitation parameter, for which the spherical aberration constant is smallest. Taking account of the dependence of the maximum obtainable axial field strength H o on the maximum field strength H p in the pole piece gap, one finds that there is an optimum design of electron microscope objective lens of conventional type which gives a lowest value of spherical aberration and highest resolving power. A modification of this optimum lens as adapted for practical use is described.