How to set the ISO sensitivity ratings for your camera

One of the variables that determines the amount of light that exposes the image sensor (the equivalent counterpart to film in a film camera) is the ISO setting. In earlier days, the ISO setting was known as the ASA film speed. You could then, and you can now, still purchase film that has ISO (or ASA) ratings from 50 to 800 or even 1,600 or 3,200. The higher the ISO rating, the more sensitive the image sensor is to light.

Changing the ISO sensitivity setting is like so many of the other settings on a digital camera — it offers trade-offs. Some trade-offs you may like, and some, depending on what you want to achieve, you won't like. The lower the ISO sensitivity (50 or 100), the less digital noise (the equivalent to 'grain' when using a film camera) you will have. As the ISO rating goes up, your photos will have more digital noise.

You can make a decision on what ISO setting to use by asking yourself four questions:

• Do you want to avoid having digital noise in your photo, or might it be considered a 'feature' of your photo?
• Does your scene or subject have enough light to use a low ISO setting?
• How much digital noise does your digital camera create at different ISO settings?
• Can you stop movement in the image and shoot without camera movement to avoid blurring the image, or is an intentional blur with a lower ISO setting something that you want?

Before making a final decision on which ISO settings are too 'grainy' for your photos, shoot a few shots with different ISO settings and compare them yourself. After you've answered these questions, you will know what ISO setting to use.

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