A retarding field scanning electron microscope for imaging a specimen provided in a specimen plane, comprising: 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; a combined magnetic-electrostatic objective 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 comprises: a 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; and a voltage supply 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; characterized in that the second electrode comprises: a substrate (131, 231); a through hole (132, 232) extending through the substrate (131, 231); and an electrode unit (133, 233) surrounding the through hole (132, 232) wherein the electrode unit is formed on a surface of the substrate; the retarding field scanning electron microscope further comprising: an electrical connection (234, 235) for connecting the electrode unit (133, 233) with the voltage supply, the electrode unit (132, 232) comprising a lower specific electrical resistivity than the substrate (131, 231). 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; a combined magnetic-electrostatic objective 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 comprises: a 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; and a 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; and a voltage supply 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; characterized in that the second electrode comprises: a substrate (131, 231); a through hole (132, 232) extending through the substrate (131, 231); and an electrode unit (133, 233) surrounding the through hole (132, 232) wherein the electrode unit is formed on a surface of the substrate; a substrate (131, 231); a through hole (132, 232) extending through the substrate (131, 231); and an electrode unit (133, 233) surrounding the through hole (132, 232) wherein the electrode unit is formed on a surface of the substrate; an electrical connection (234, 235) for connecting the electrode unit (133, 233) with the voltage supply, the electrode unit (132, 232) comprising a lower specific electrical resistivity than the substrate (131, 231).