Sometimes when shooting in low light, you will want to use a long exposure, such as when photographing fireworks, star trails (Figure 7.11), or car headlights moving down a street. For this kind of photography, a sturdy tripod is a must. It is also a good idea to use a cable release (see Chapter 3) or the self-timer to help prevent the camera shake that occurs when you press the shutter button.
When your camera is stabilized on a tripod, you shouldn’t normally need to use a high ISO. Your goal should be to use a low ISO (typically from 100 to 400) to reduce noise. As we discussed in Chapter 6, a long exposure on its own can add a bit of noise to your image, so minimizing the additional noise from a high ISO is recommended.
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