A scanning pattern generator and a method for microlithographic multi-beam writing of high precision patterns on a photosensitive substrate (11), the system comprising a light source (1), preferably a laser, for generating at least two light beams, a computer-controlled light modulator (4), a deflector for scanning the beams on the substrate and an objective lens (10) to contract the at least one light beam from the light source before it reaches the substrate, wherein at least the objective lens is arranged on a carrier (22) being movable relative to the substrate (11) and the light source (1). Hereby, the carrier defines a movable optical path relative to the remaining, stationary optical path. Further, the system comprises means for altering the stationary optical path in order to maintain telecentricity for the beams as they impinge on the photosensitive substrate during the movement of the carrier and the movable optical path.