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Step 1
Determine how much light the picture will need. Because the ISO determines how sensitive the image sensor will be to the light source, in brighter conditions you will want to set your ISO to a low setting while dark conditions will require a higher setting. However, the higher you set the ISO, the more likely the photo will become grainy.
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Step 2
Set your other digital camera settings such as the aperture (how wide the lens opens) and the shutter speed (how long the lens stays open).
On some digital camera models, you can use the Automatic Exposure (AE) program to set these features for you. You determine the ISO, and the camera will determine the shutter speed and aperture. To change the camera to AE, change the mode dial to "P." For example, on a Canon Digital Rebel, this dial is on the top right. -
Step 3
Set your ISO speed. To do this on a Rebel, press and hold the "ISO" button (the up arrow on the back of the camera) and rotate the main dial until the desired ISO displays in the LCD panel. To set the ISO in other camera models, refer to your user's manual.
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Step 4
Take the picture. With your ISO, shutter speed and aperture set, you can take your picture. Note that if you are using a higher ISO speed, using a tripod may reduce some of the noise.
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Step 5
Continue to practice taking photos using different ISO settings. The great thing about ISO in a digital camera is that you're not wasting film as you experiment. You may want to start with the AE program until you have practiced changing the ISO a couple of times.
