Lens Stabilisation (Optical IS)
Lens stabilisation is a moving part inside the lens that cancels small hand shake, so you get sharper handheld photos and steadier video in dim light.
On this page 3 sections
Lens stabilisation, also called optical image stabilisation, optical IS or OIS, is built into the lens itself. When the camera shakes slightly, a group of glass elements inside the lens shifts to cancel the movement, so the image stays steady on the sensor. This allows sharp handheld photos at slower shutter speeds, which matters indoors, at dusk and with zoom lenses.
How it works
Gyroscopic sensors in the lens detect the shake. Small motors then move a floating lens group in the opposite direction, so the light reaches the sensor along a steady path. Because the system is in the lens, it works only with that lens.
How it relates to the camera body
Some bodies have their own stabilisation. If both are present, many cameras let the two work together for steadier results. If the body has none, the lens is the only stabilisation.
What it does not promise
It does not freeze a moving subject, which needs a fast shutter whatever the lens. It does not replace a tripod for long exposures at night. It adds to the size and weight of a lens, and a lens without it gives no stabilisation unless the body has its own.