The term shutter speed refers to the length of your exposure, usually in mere fractions of a second. Shutter speeds typically range from the ultra-fast 1/8000th of a second to the long and dreamy 30 seconds.

The shutter speed you use, coupled with the aperture setting on your lens, controls the amount of light let in to your sensor. The shutter speed does this by controlling how much time the sensor "sees" the scene. If your shutter speed is 1/250th of a second, then your sensor will capture the light it sees in just that exact 1/250th of a second. The longer your shutter speed, the more light.

Exposure

Shutter speeds are divided into stops. Going down the scale to longer speeds, each stop lets in twice as much light as the one before it. For example, the shutter speed 1/60th of a second gives you twice the light as 1/125th of a second. Going up the scale to shorter speeds, each stop lets in half as much light as the one before it. (On most modern cameras, these stops are broken down into half-stops or third-stops, allowing for greater exposure accuracy.)

In every photo situation, you have a variety of shutter speed settings that will result in a perfect exposure. You're never locked into one speed. Because as you let in more light with slower shutter speeds, you can close off the amount of light coming through the lens with your aperture setting. So if your meter tells you that the proper exposure is 1/250th of a second at the aperture f4.0, you can also shoot at 1/125th @ f5.6, 1/60th @ f8, 1/30th @ f11, 1/15th @f16, 1/8th @ f22, and on and on.

The Shutter Speed Effect

Shutter speed and aperture settings have a direct effect on the look of your photographs. While your aperture setting controls your depth of field (how much of your scene, front to back, is in focus), the shutter speed is more about freezing time and motion. For example, shutter speeds 1/1000th of a second and higher are used by sports photographers to freeze action.

Shutter Speeds and Lenses

One thing to keep in mind when setting your shutter speed is lens shake. If you are hand-holding the camera during exposure, there will be some amount of shake. It's not humanly possible to hold a camera as still as a tripod. And the longer your lens, the more pronounced this shaking will be. The general rule is to use a shutter speed higher than the focal length of the lens.

So if you're using a 100mm lens, try to shoot at 1/125th or higher. Using a 50mm lens, try to shoot at 1/60th of higher. Using a 200mm lens, try to shoot at 1/250th or higher. As you get used to your equipment, you will find out just how steady you are and adjust the rule to fit your needs. You may find you can hand-hold your camera for longer than the rule would indicate.