Shutter speed: how to freeze or blur motion

Shutter speed is how long the sensor collects light for one picture. It is written as a fraction of a second: 1/1000 is very fast, 1/30 is slow, and 2 seconds is a long exposure. It controls two things: how bright the picture is, and how movement looks.

A faster shutter freezes movement; a slower one lets it smear. As a rough guide:

• 1/60 s: a person standing still, if you hold the camera steadily.
• 1/250 s: people walking, children playing.
• 1/1000 s: running, cycling, most sport.
• 1/2000 s or faster: birds in flight and fast action.

When you hold the camera, even a still subject blurs if the shutter is too slow. A good rule of thumb is to use a shutter speed of at least one over the focal length: 1/50 s or faster for a 50 mm lens, 1/200 s for a 200 mm lens. Image stabilisation can give you several stops of margin, and a tripod removes the problem for still scenes.

Slow shutters are a creative tool. On a tripod, a half-second or longer turns running water silky and lights into streaks. Panning, which means following a moving subject with the camera at around 1/30 s, keeps the subject fairly sharp against a streaked background. In bright daylight you will need a neutral density filter to reach these speeds without overexposing.

Shutter speed is one third of the exposure triangle, together with aperture and ISO. If you slow the shutter by one stop you let in twice as much light, so you can close the aperture or lower the ISO by one stop to keep the same exposure.