Abstract: A variable magnification scanning optical system for a copying machine includes a lens (10) for projecting an image of an original document (2) with a pre-selected magnification onto a moving imaging member (6). The scan speed may be varied relative to the speed of the imaging member to alter the magnification in the scan direction. To this end a reference signal is generated which is derived from the imaging member and is indicative of the nominal pre-selected magnification. A second signal is generated indicative of the scan speed and the scan speed is varied, e.g. by a servo system (see FIG. 2), until the second signal matches the reference signal. To compensate for tolerances between the nominal magnification and the actual magnification, the reference signal may be adjusted by applying an offset value (23) stored in the memory. This offset value may be entered into the memory by an operator via a keyboard panel (22).