The invention provides a focussing electron beam device with a single or an array of field emitter beam sources to generate electron beams with field emitter beam sources, at least one anode capable of accelerating the electrons of the electron beams towards a specimen, focussing components capable of focussing the electron beams onto the specimen and a control circuit that a) senses for deviations of the actual current values of the electron beams from desired current values; b) controls first voltages V1 to adjust the actual current values of the electron beams to the desired current values and c) controls second voltages V2 to adjust the actual focus positions of the electron beams to the desired focus positions. The voltage control circuit adjusts the actual current values of the electron beams to the desired current values and makes it possible to adjust the current values of an array of electron beams to a single value. Furthermore, a focussing electron beam device is disclosed with an array of field emitter beam sources integrated onto a substrate, which makes it possible to have arrays of field emitter beam sources with thousands or even millions of field emitter beam sources. With the integration of the control circuits for each field emitter beam source it is possible to adjust the current values and focus positions of each electron beam individually. Furthermore, methods are disclosed describing the operation of a single field emitter beam source or an array of field emitter beam sources.