This product is an ultra-telephoto zoom lens covering a telephoto range up to 500 mm, incorporating Sigma's original OS (Optical Stabilizer) 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 stabilizer lens group to effectively compensate for camera shake. It offers the use of shutter speeds approximately 4 stops slower. Mode 1 is ideal for general photography, and Mode 2 is effective on moving subject such as motor sports and so on.