An electrostatic optical system has been designed to produce a high resolution (10–100 nm) ion beam probe based on a very high brightness H+2field ionization source developed in our laboratory.1The system described here includes two electrostatic lenses, postlens octupole and quadrupole deflectors, beam blanker, stigmation and alignment deflectors. Since the resolution of this system is limited by the aberrations of the optics, a systematic approach is employed to minimize these aberrations. First, individual lenses were designed by many trial evaluations using appropriately constructed figures of merit. The scales and magnifications of both lenses then were determined simultaneously to minimize the axial aberrations of the combined lens. The deflectors were also optimized using analytical expressions of deflection aberration coefficients to achieve small deflection aberrations. The beam blanker at the beam crossover point can also give reasonably high blanking rates (10–300 MHz) for H+2ions with small spurious deflection. This optical system is to be used in an ion beam lithography machine currently under construction. In this system, a 2 mrad beam acceptance half‐angle will produce a probe size of 10 nm with a current density of 100 A/cm2at 50 keV energy when used with the H+2field ion source which produces a typical angular current density of 10 μA/sr.