The ISO setting in your camera allows you to choose the level of sensitivity of the camera sensor to light. The ability to change this sensitivity is one of the biggest advantages to using a digital camera. In the days of film cameras, you had to choose the ISO by film type. This meant that if you wanted to shoot in lower light, you had to replace the film in the camera with one that had a higher ISO. So not only did you have to carry different types of film, but you also had to remove one roll from the camera to replace it with another, even if you hadn’t used up the current roll. Now all you have to do is go to your information screen and select the appropriate ISO.
Having this flexibility is powerful, but just as with the quality setting, the ISO setting has a direct bearing on the quality of the final image. The higher the ISO, the more digital noise the image will contain. Since our goal is to produce high-quality photographs, it is important to get control over all of the camera settings and bend them to our will. When you turn your camera on for the first time, the ISO will be set to Auto. This means that the camera is determining how much light is available and will choose what it believes is the correct ISO setting. Since you want to use the lowest ISO possible, you will need to turn this setting off and manually select the appropriate ISO.
Which ISO you choose depends on your level of available or ambient light. For sunny days or very bright scenes, use a low ISO such as 100. As the level of light is reduced, raise the ISO level. Cloudy days or indoor scenes might require you to use ISO 400 (Figure 1.4). Lowlight scenes, such as when you are shooting at night, will mean you need to bump up
that ISO to as high as 1600. The thing to remember is to shoot with the lowest setting possible for maximum quality.
Setting the ISO
Press and hold the ISO button on the back of the camera while rotating the Command dial to select ISO Sensitivity based on available light, and release the button when you have made your selection.
You should know that the Auto ISO option is enabled as a default only when using one of the automatic scene modes. When using one of the professional modes, the Auto ISO feature will be automatically turned off. If you wish to use Auto ISO in one of these modes, you must activate it and set the auto parameters in the shooting menu. If you plan on shooting with the Auto mode, you cannot turn off the Auto ISO option at all.