Many digital cameras offer a choice of ISO settings, which indicate the light sensitivity of the camera’s imaging sensor. The higher the ISO number, the more quickly the camera reacts to light. A high ISO setting increases light sensitivity, but it can also add noise to the picture.
This figure shows four images taken with a different ISO setting for each shot: 200, 400, 800, and 1600.
For some shooting scenarios, you may be forced to use a higher ISO. For example, if you’re trying to capture a moving subject, you may need to raise the ISO so that you can use the fast shutter speed necessary to freeze the action.
Experiment with ISO settings if your camera offers them. But, for best picture quality, keep the ISO at its lowest or next-to-lowest setting.