The device comprises a source of lighting (20) creating an illuminating beam (3) using an arrangement of illuminating lenses (4) and an observation beam (11) using an arrangement of observation lenses (12). Field apertures (2) are positioned in each of the beams (3,11) meeting the image plane (6) in an acute angle. Both beams (3,11) are intersected by a single light-reflecting and swivel mounted mirror element (14) performing an oscillating motion. The element (14) is part of a mirror galvanometer.
