The LowDown on ISO

ISO is the number signifying the light sensitivity of an imaging sensor; it is measured in numbers (like 100, 200, 400, 800 etc). Sometimes, this number is also known as an "ISO number", or, more commonly, the "film speed". 

Historically, the lower the ISO number, the lower the sensitivity of the film and the finer the grain in the pictures or shots you are taking. This has translated pretty well into digital photography, too: Higher ISO gives you higher sensitivity, but at the cost of a larger amount of digital noise.

• You obtain the best image quality by using the lowest ISO possible on your digital camera. If you want to ensure your digital camera always uses the lowest ISO setting, switch the ISO setting from the default "Auto ISO" (this setting is usually found in the Menu) to the lowest possible on the camera, say ISO 50.

• If you mostly take pictures where there is enough light for a correct exposure, i.e. sunny outdoors, then using the lowest ISO on your digital camera will give you the best image quality your digital camera is capable of.

• If you want to take pictures indoors where light may not be sufficient and in other low-light situations, then you would need to supplement existing light with flash or studio lights. Either that, or select a higher ISO. Of course, depending on your digital camera, a higher ISO may mean a noisy image.

• If you leave your camera on "Auto ISO" and if you find that most of your images are noisy, then perhaps you are taking most of your pictures in low-light situations where the camera has automatically selected a higher ISO.