An operating or surgical microscope is an optical instrument that provides the surgeon with a stereoscopic, high quality magnified and illuminated image of the small structures in the surgical area. The optical components of a basic stereo microscope consist of the binocular head, a magnification changer, the objective lens and an illuminator which beams light through the objective lens and onto the operating field. The magnification can be changed by turning a knob (which selects different magnification lenses) or by using a motorized zoom controlled by a foot pedal.