Abstract: An electron beam apparatus in which the electron beam is directed to a sample and secondary electrons from the sample return in the direction of the beam and are deflected sideways to a collector by a first electrostatic deflection means. To compensate for distortion of the spot produced by the beam as a result of the first electrostatic deflection means, a similar deflection means is placed above the first means to correct the distortion and is so biased as to reflect secondary electrons which might otherwise pass the first means. The deflection means are 4-pole electrostatic stigmators. A threshold grid is biased to allow to pass to the first means only those secondary electrons having release speeds from the sample above a certain value.