An optical image stabiliser is a system which compensates for camera shake, so as to reduce the incidence of blurry photos in handheld photography. In Canon cameras
, this is achieved by analysing movement with gyro sensors, then shifting a lens element within the lens to correct the light path. The benefit of this is that the photographer can shoot at speeds up to 4 ‘stop’s slower (depending on product), and still get a sharp shot. You can tell that a Canon lens has a stabilizer by the initials ‘IS’ in the name.