ISO

This is a great explanation of ISO . As is this...

When choosing the ISO setting I generally ask myself the following four questions:

1. Light – Is the subject well lit?
2. Grain – Do I want a grainy shot or one without noise?
3. Tripod – Am I use a tripod?
4. Moving Subject – Is my subject moving or stationary?

If there is plenty of light, I want little grain, I’m using a tripod and my subject is stationary I will generally use a pretty low ISO rating.