Abstract: particle-optical apparatus at a comparatively low acceleration voltage (from 0.5 kV to 5 kV). This lens defect cannot be eliminated by means of rotationally-symmetrical fields. In order to enhance the resolution nevertheless, it has already been proposed to mitigate said lens defect by means of a corrector of the Wien type. This known configuration consists of a number of electrical and magnetic multipoles. In order to adapt the corrective capacity of the corrector 28 to the strength of the objective 8 to be corrected and to achieve less severe requirements in respect of mechanical tolerances, according to the invention the corrector 28 is excited in such a manner that the trajectory of the electrons constitutes a sinusoid of a length which does not deviate more than 10% from a full sine period, upstream and downstream from the correction device there being arranged an n-pole, where n=4, 6, . . . (27, 29), at a distance which is less than ¼ of the length of the corrector.