You can use the ISO control built into your digital camera to vary its sensitivity to light and thus
mimic the effect of using different grades of 35mm film. This can come in handy in a number of
situations, such as when you’re shooting in particularly high- or low-light situations. Remember
a few key facts about your digital camera’s ISO ratings, though:
■ It’s not a real ISO adjustment, in the sense that your camera doesn’t have real film. Each
camera maker has a somewhat different way of implementing this feature, but they all
use ISO numbers since that’s the same as the ISO numbers used by 35mm film.
■ Don’t leave your camera set at the highest ISO all the time. Some folks think that by
setting their cameras to the highest sensitivity, they’ll be prepared for anything and won’t
have to muck with the camera menu when they’re on the go, trying to take pictures. In
reality, boosting your camera’s sensitivity to light also increases the amount of digital
noise you’re capturing. More ISO means more fringing, artifacts, and digital detritus, as
in the image shown in the following illustration. Sometimes that’s unavoidable, but stick
with the lowest ISO value you can get away with most of the time. To do that, set your
camera’s ISO control to its lowest setting.