ISO in digital photography measures the sensitivity of the image sensor. The lower the ISO number, the less sensitive your camera is to light and there’s less grain. Higher ISO numbers are used in darker settings.
When choosing ISO settings, pay attention to the surrounding light. If there’s plenty of light, use a low ISO setting.
If you want a clear shot without any grain, also shoot with a low ISO.
Be aware if your subject is in movement or stationary. If your subject is moving, increase the ISO to shoot with a faster shutter speed to capture the action.
The negative aspect of increasing your ISO is that the photos will become grainier.
There are some situations where you do need higher ISO settings. These include:
-Indoor sports events: fast-moving subject with limited light
-Concerts: low light with no flash
-Galleries/Churches: low light with rules against flash
Rowse, Darren. “ISO Settings in Digital Photography – Digital Photography School.” Digital Photography School RSS. Digital Photography School, n.d. Web. 1 May 2014. <http://digital-photography-school.com/iso-settings/>.