Multiple electron beamlets are split from a single electron beam. The electron beam passes through an acceleration tube, a beam-limiting aperture, an anode disposed between an electron beam source and the acceleration tube, a focusing lens downstream from the beam-limiting aperture, and a micro aperture array downstream from the acceleration tube. The micro aperture array generates beamlets from the electron beam. The electron beam can be focused from a divergent illumination beam into a telecentric illumination beam.