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The shutter speed controls for how long the sensor is exposed. When a subject is moving, the natural desire for most photographers is to freeze the action. This is appropriate for many sporting events, whether it's a footballer running towards you or a tennis player serving the ball. It's an equally appropriate response to capture a brief moment in time that may be missed by the human eye, such as a balloon exploding.

The first half of the challenge is selecting a quick enough shutter speed to freeze the action. Generally speaking, fast action will require a shutter speed of at least 250th of a second, or 1⁄250. To stop something in its tracks completely you may need something faster still, such as 1,000th of a second, or 1⁄1,000.

To adjust the shutter speed, simply put your camera into Shutter Priority mode and it will find an aperture to match. As the shutter speed becomes faster, the amount of light entering the camera decreases and you or your camera will need to open the aperture or increase the sensitivity to compensate.

The other half of the challenge is your timing. You should get to know your camera and how long it takes between pressing the button and it actually capturing the photo. Some compact cameras can be quite slow, but if you can anticipate when the ideal moment is going to take place, you can always press the button fractionally in advance.

Another trick is to select your camera's continuous-shooting option and just keep the button pressed down as the action takes place. Your camera will then take several photos in quick succession and with any luck at least one will look great.

Sometimes, freezing the action can produce lifeless images. We know from childhood art classes that blurred objects look as if they're moving quickly, so why not emulate the effect in photography? Instead of a quick shutter speed, go for a relatively slow one such as a 30th of a second, or 1⁄30. Anything in motion will become blurred, and this effect can look great with waterfalls, for example.

A particularly effective trick is to choose a slow shutter speed, then move your camera to follow a subject zooming past as you take the photo. If you keep the subject in the middle of the screen or viewfinder it will remain relatively sharp, but the background will become blurred, lending the effect of speed. This is a great trick when photographing races or airshows.

	1 Fast shutter speeds will freeze action, but it's not always the best technique.

	2 Use slower shutter speeds to blur action and make water look dream-like.