Click to explore how image stabilization reduces but doesn't eliminate blur caused by camera movement.

When you move the camera during an exposure, especially at slow shutter speeds, when shooting close-ups, or using a long focal length lens, it causes blur in the image. To reduce this blur, some cameras have image stabilization systems. These systems use a sensor to recognize camera movement and then try to compensate using a variety of techniques. The process goes under a confusing variety of names including image stabilization, vibration reduction, and anti-shake. Manufacturers claim 2 to 3 stop increases before camera shake blurs an image. This means that if you can shoot safely at 1/60 without IS, you can shoot at 1/15 or even slower with it.

• Optical image stabilization works by moving a prism in the camera or an element in the lens to redirect the light path to compensate for the unintended movement. The camera moves one way, and the prism or lens element moves the other. This is the most effective method, but also the most expensive.
• Digital image stabilization shifts the image on the sensor to compensate for motion. It's like watching a baseball infielder moving around to stay under a windblown pop-up. When this technique is used, not all of the sensor's pixels can be used for the image. Some of those on the border have to be reserved for the shifting image projected by the lens. Another digital technique is to process the captured image to try to remove the blur.
• Pseudo image stabilization just increases the ISO so the camera can select a faster shutter speed.

When the camera has a fixed lens, it doesn't matter which approach is used. However, on cameras with interchangeable lenses it does matter. If the system resides within the camera body it will work with any lens, if it resides within the lens it only works with special lenses.

When thinking about image stabilization, keep in mind that it's always been available in the form of a tripod, monopod, beanbag, or a flat surface on which to rest the camera. You can increase stability by using the self-timer or remote and mirror lockup to reduce vibrations.