A charged particle system comprises a particle source for generating a beam of charged particles and a particle-optical projection system. The particle-optical projection system comprises a focusing first magnetic lens (403) comprising an outer pole piece (411) having a radial inner end (411′), and an inner pole piece (412) having a lowermost end (412′) disposed closest to the radial inner end of the outer pole piece, a gap being formed by those; a focusing electrostatic lens (450) having at least a first electrode (451) and a second electrode (450) disposed in a region of the gap; and a controller (C) configured to control a focusing power of the first electrostatic lens based on a signal indicative of a distance of a surface of a substrate from a portion of the first magnetic lens disposed closest to the substrate.