Like the aperture setting, the shutter speed you choose isn’t simply a way of controlling the overall exposure. It also has a visible effect on your shots, enabling you to control the appearance of a moving subject.
Fast shutter speeds freeze movement, ensuring pin-sharp pictures no matter how unsteady your grip on the camera, or how fast the subject is moving. Slow shutter speeds tend to blur movement, and so can be used for creative effects. Generally speaking, the slower the shutter speed, the greater the degree of motion blur in the image you take.
The shutter speed is the length of time that the shutter is left open. The scale used is easier to understand than the aperture system, because speeds are measured in fractions of a second. However, the numbers are often simplified – so 1/125 sec is shown as 125, 1/15 sec as 15 and so on. Speeds of a second or longer are shown as 1”, 2”, and so on.
Working in stops
As we’ve established, your aperture and shutter speed work together to capture an exposure. This means that there is no one single combination that will give you the correct exposure. You can pair a slow shutter speed with a narrow aperture, or a fast shutter speed with a wide aperture, and get a shot that is equally as bright. In the following sequence, 1/125 sec at f/5.6, 1/60 sec at f/8 and 1/30 sec at f/11 will all let in the same amount of light to produce an identical exposure.
Each f-stop number is ‘half’ the size of the one before it, and so lets in half as much light. The difference between two sequential f-stop numbers is often referred to as an f-stop, or simply a ‘stop’. If you reduce the aperture by one stop (letting less light in), to set the same exposure you need to compensate by slowing the shutter speed by one stop, to allow that light to hit the sensor for twice as long. Unless you’re in manual mode, your SLR will work this out for you.
Keep up to speed
If you’re shooting handheld (without a tripod) you’ll need a fast enough shutter speed to make sure camera shake doesn’t cause blurred shots. A good rule of thumb is to use a shutter speed that’s faster than the focal length on your lens; so with a focal length of 200mm, make sure you shoot at around 1/250 sec or faster.
The more you zoom in, the faster the shutter speed will need to be. Keep an eye on the shutter speed in the viewfinder and widen the aperture if necessary. In low light, you may need to increase the ISO, or use a tripod, which will allow you to shoot at very slow shutter speeds.
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