The Sigma Lenses 18-125mm f/3.8-5.6 DC OS HSM is equipped with Sigma's own unique OS (Optical Stabiliser) function. This function uses two sensors inside the lens to detect vertical and horizontal movement of the camera and works by moving an optical image stabilizing lens group to effectively compensate for camera shake. This system offers the use of shutter speeds approximately 4 stops slower. It also automatically detects movement of the camera and compensate for camera shake when shooting moving subjects such as motor sports.