An optical system has a rotary scanning mirror, an optical instrument and an optical image rotation device. The rotary scanning mirror receives an incident beam of rays and returns an input beam along a first axis. The optical instrument receives the input beam from the scanning mirror and returns an output beam parallel to the input beam along a second axis in a direction opposite to the input beam towards the optical rotation device. The optical image rotation device is positioned on the second axis and receives the output beam. The scanning mirror has an axis of rotation aligned on the first axis. The optical image rotation device has an axis of rotation aligned on the second axis. The optical system comprises a common driving device for rotationally driving the optical image rotation device and the scanning mirror about their respective rotation axes.