An aperture array for a multi-beam array system and a method of selecting a subset of a beam from a multi-beam array system are provided. The aperture array comprises an array body arranged proximate to a beam source. The array body comprises a plurality of apertures, at least two of the apertures having different geometries. The array body is movable, via an actuator, relative to an optical axis of the beam source, such that a subset of a beam from the beam source is selected based on the geometry of the aperture that is intersected by the optical axis.