I keep my ISO on 100 unless I need to hand hold the camera or stop motion. ISO is film speed basically. Generally speaking the higher the ISO the more noise you will notice in your pictures.
If you don't have a tripod you'll want to try and keep your shutter speed higher than your lens' focal length. Any less and you'll start to see blurry pictures from your hand shaking.
Aperture serves two major purposes when composing a shot. Depth of field as described by the above poster is one. The other is how much light you are letting into the camera. The smaller the number (1.4 for example) the wider the lens is opened and the more light you let in. The larger the number (f22 for example) the less light.
More light = faster shutter speeds
Less light = slower shutter speeds
Shutter speed = how fast the camera takes the picture.
So to answer your questions directly...
I change my ISO and AV constantly depending on what type of picture I want and what the situation is. I don't have a set rule.
Reply With Quote