A scanning apparatus for use in a scanning optical system comprises a laser transmitter to produce a transmitter beam. This transmitter beam is deviated by a beam scanner, e.g. a tiltable mirror, to produce a pattern of a scanning beam. There are bearings which define first and second axes of rotation perpendicular to each other and intersecting each other in an intersecting point for allowing the beam scanner to scan. In front of the beam scanner is a window of transparent material in the shape of a spherical cap so as to define a central axis and a central point. The central axis intersects the intersecting point of the two other axes, and this common intersecting point coincides preferably with the central point of the sphere of the window.