A probe forming electron optical system utilizing Schottky field emission cathode technology has been designed and optimized for application to high spatial resolution scanning Auger microscopy (SAM). This article examines optics design trade-offs driven by the unique requirements of SAM, summarizes the theoretical performance limits of the resulting design, and compares simulation and experimental results over a wide range of operating conditions. Experimental results reported include beam diameter as a function of voltage and current, and beam current stability in various modes of operation (less than or similar 1%/h under optimum conditions). Experimental beam size data are compared to limits set by the magnified source, spherical and chromatic aberration, deflection aberrations, diffraction and space charge effects. The optical system, is designed to operate at beam voltages ranging from < 1 to 25 kV, with beam current at the sample of < 1-100 nA. The operational mode of the instrument is chosen to emphasize either high spatial resolution (at the expense of maximum current) or high throughput (at the expense of spatial resolution) under the discretion of the operator. Switching from one to the other is accomplished by a change in the voltage applied to the extraction anode, resulting in the desired angular emission intensity J(OMEGA). The time required for stabilization of the source after such a change has been found to be acceptable; for example, following a change from 0.25 to 1.0 mA/sr, beam current drift of less than or similar 2%/h is generally achieved in less than 60 min.