A retarding field scanning electron microscope for imaging a specimen is described. The microscope includes a scanning deflection assembly configured for scanning an electron beam over the specimen, one or more controllers in communication with the scanning deflection assembly for controlling a scanning pattern of the electron beam, and a combined magnetic-electrostatic objection lens configured for focusing the electron beam, wherein the objective lens includes a magnetic lens portion and an electrostatic lens portion. The electrostatic lens portion includes an first electrode configured to be biased to a high potential, and a second electrode disposed between the first electrode and the specimen plane, the second electrode being configured to be biased to a potential lower than the first electrode, wherein the second electrode is configured for providing a retarding field of the retarding field scanning electron microscope. The retarding field scanning electron microscope further includes a voltage supply being connected to the second electrode for biasing the second electrode to a potential and being in communication with the one or more controllers, wherein the one or more controllers synchronize a variation of the potential of the second electrode with the scanning pattern of the electron beam.