An image stabilizer is used to get sharp photos at slow shutter speeds which would normally be spoiled by camera shake. The minimum ‘safe’ shutter speed depends on the conditions and the lens you’re using, but an image stabilizer can let you use shutter speeds up to five stops slower – or more.
Image stabilizers work by detecting any camera movement during the exposure using gyroscopic sensors, then instantly compensate for this movement.
Image stabilizers are built into many lenses. When movement is detected, a ‘floating’ group of lenses shifts to compensate so that the image on the sensor stays steady. Many Canon lenses have ‘IS’ in the name, which stands for ‘Image Stabilizer’. Nikon calls its system VR (Vibration Reduction) and other camera and lens makers offer lens-based stabilisers too, using their own names but very similar technologies.
Increasingly, though, camera makers are building image stabilisers into the camera itself. Here, the camera sensor is moved to compensate for any camera movement. This is often called in-body image stabilization, or IBIS. The sensor movement can be quite complex, and the best systems offer 5-axis stabilization, where the sensor can be instantly shifted in five different axes of movement.
A few camera systems now use dual image stabilization systems, with image stabilizers in both the lens and the camera body. These work together to offer even more effective stabilization.
Makers quote the effectiveness of image stabilizers using shutter speed or exposure values. Typically, an image stabilizer might offer 3-5 stops of shake compensation. With a 5-stop stabilizer, this means that where you might normally expect to have to use a shutter speed of 1/250sec to get a sharp shot with a particular lens, for example, you should be about to get sharp shots at shutter speeds as low as 1/8sec.
Image stabilizers do increase your chances of getting sharp shots at slower shutter speeds, but there are no guarantees. Some are more effective than others and it’s best to think of them simply as extra insurance against camera shake. Testing body CIPA does test manufacturers’ claims, but very often the maximum shake compensation figure quoted is in very specific conditions with a particular lens.
Any image stabilizer than uses moving elements in a lens or an in-body stabilization system is an ‘optical stabilizer’. This is because the image is being shifted optically to keep it steady on the sensor. This is the best type of stabilization, but some cameras also offer ‘digital stabilization’ or ‘electronic stabilization’.
You often find this on cheap point and shoot cameras, and it’s a poor substitute for optical stabilization.
But it’s also offered on may higher-end cameras which shoot video, and here, digital stabilization is much more effective because it can check the subject alignment between frames and adjust the camera framing/cropping to correct any shift in the camera position. Digital stabilization is a known and useful technique in video, and some cameras use it alongside regular optical stabilization. The only drawback is that the framing is cropped somewhat to allow enough leeway to compensate for movement.