When shooting most landscape scenes, the ISO is the one factor that should only be increased as a last resort. While it is easy to select a higher ISO to get a smaller aperture, the noise that it can introduce into your images can be quite harmful. The noise is not only visible as large grainy artifacts; it can also be multicolored, which further degrades the image quality.
When shooting landscapes, set your ISO to the lowest possible setting at all times (Figure 7.3). Between the use of Vibration Reduction lenses (if you are shooting handheld) and a good tripod, you will seldom need to shoot landscapes with anything above an ISO of 400.