Abstract: In order to reduce object contamination during the examination or machining of the object in an electron beam apparatus, an anti-contamination diaphragm is provided in place of the customary diaphragm. The anti-contamination diaphragm has a central aperture which corresponds to a customary diaphragm aperture, and a concentric annular aperture for transmitting a non-paraxial hollow beam which irradiates a ring around the paraxial focus on the object. The conical hollow anti-contamination beam forms a barrier against contaminating residual gas molecules, notably hydrocarbon molecules.