Systems and methods are provided for compensating dispersion of a beam separator in a single-beam or multi-beam apparatus. Embodiments of the present disclosure provide a dispersion device comprising an electrostatic deflector and a magnetic deflector configured to induce a beam dispersion set to cancel the dispersion generated by the beam separator. The combination of the electrostatic deflector and the magnetic deflector can be used to keep the deflection angle due to the dispersion device unchanged when the induced beam dispersion is changed to compensate for a change in the dispersion generated by the beam separator. In some embodiments, the deflection angle due to the dispersion device can be controlled to be zero and there is no change in primary beam axis due to the dispersion device.