An optical system including a plurality of selectably directable mirrors (38) each arranged to direct a laser beam (41) to a selectable location within a field, a plurality of mirror orientation sensors (45) operative to sense the orientation of the plurality of selectably directable mirrors and to provide mirror orientation outputs and an automatic calibration subsystem (47) for automatically calibrating the plurality of selectably directable mirrors, the automatic calibration subsystem including a target (40) being operative to provide an optically visible indication of impingement of a laser beam thereon; the target being rewritable and having optically visible fiducial markings (54, 56), a target positioner (42) for selectably positioning the target, an optical sensor (44) operative to view the target following impingement of the laser beam thereon and to provide laser beam impingement outputs and a correlator (36) operative to provide a calibration output.