A multi-beam pattern definition device (102) for use in a particle-beam processing or inspection apparatus is configured to be irradiated with a beam (lp,bp) of electrically charged particles so as to form a number of beamlets to be imaged to a target. An aperture array means (202) comprises at least two sets of apertures (221, 222) for defining respective beamlets (b1-b5), wherein the sets of apertures comprise a plurality of apertures arranged in interlacing arrangements and the apertures of different sets are offset to each other by a common displacement vector (d12). An opening array means (201) has a plurality of openings (210) configured for the passage of a subset of beamlets corresponding to one of the sets of apertures but lacking openings (being opaque to the beam) at locations corresponding to the other sets of apertures. A positioning means shifts the aperture array means relative to the opening array means in order to selectively bring one of the sets of apertures into alignment with the openings in the opening array means.