Camera shake is a major cause of blurred images, especially with handheld photography or in low light situations where a slow shutter speed is required.
Canon's Image Stabilizer (IS) technology uses a lens shift-type system to detect and correct slight camera shakes. Pressing the shutter button halfway releases the lock on the Image Stabilizer system. Minute gyro sensors detect lens vibrations caused by
hand shake and send a signal to a microcomputer, which controls an IS lens group that compensates for the pitch and yaw (movement along the horizontal and vertical axis of the camera) of the lens. To ensure that intentional panning and tilting isn’t
mistaken for camera shake, some telephoto and tele-zoom lenses have IS Mode 2. This mode detects if movement in a certain direction occurs for longer than a preset time and switches off the Image Stabilizer in that direction.
EF lenses with IS technology enable steady shooting at up to four stops lower than is possible with conventional lenses, making them ideal for situations where the use of flash is not permitted or desired.