The invention relates to a charged particle optical system comprising a beamlet generator for generating a plurality of charged particle beamlets, an electrostatic deflection system for deflecting the beamlets, and a projection lens system for directing the beamlets from the beamlet generator towards the target. The electrostatic deflection system comprises a first electrostatic deflector and a second electrostatic deflector for scanning charged particle beamlets over the target. The second electrostatic deflector is located behind the first electrostatic deflector so that, during operation of the system, a beamlet generated by the beamlet generator passes both of the electrostatic deflectors. During operation of the first and second electrostatic deflectors the system is adapted to apply voltages on the first electrostatic deflector and the second electrostatic deflector of opposite sign.