Many of today’s Canon lenses come with a feature called image stabilization (IS). If you happen to have one of these lenses, you have a little extra help keeping your lens stable while doing any type of handheld photography. This is extremely useful in situations where the light is low and, to prevent camera shake, you need to set your shutter speed slower than you normally would when shooting without a tripod (Figure 7.3). Most people can hold their camera steady at 1/60 of a second or faster. The longer your focal length, the faster your shutter speed needs to be in order to keep your images sharp and free of camera shake.
The Canon IS lenses contain small gyro sensors and servo-actuated optical elements that correct for camera shake and stabilize the image. The IS function is so good that it is possible to improve your handheld photography by two or three stops, meaning that if you are pretty solid at a shutter speed of 1/60, the IS feature lets you shoot at 1/15, and possibly even 1/8 of a second (Figures 7.4 and 7.5).