An improved aperture arrangement in a device for defining a pattern on a target, for use in a particle-beam exposure apparatus, by being irradiated with a beam of electrically charged particles and allowing passage of the beam only through a plurality of apertures. The device includes an aperture array having a plurality of apertures of identical shape defining the shape and relative position of beamlets permeating the apertures. A blanking device switches off the passage of selected beamlets permeating the apertures and defined by them. The apertures are arranged on the aperture array according to an arrangement deviating from a regular arrangement by small deviations, adjusting for distortions caused by the particle-beam exposure apparatus, and the size of the apertures of the aperture array differs across the aperture array in order to allow for an adjustment of the current radiated on the target through the apertures and the corresponding openings.