Understanding ISO

Low ISO                                          

ISO-100
Aperture-f/4.0
Shutter Speed-1/25

High ISO
ISO-6400                          

Aperture-f/4.0
Shutter Speed-1/500














1) ISO is how much light comes through.
2) ISO works technically because it will do it by itself and fix the lighting so it looks better and visually is so the picture itself looks good.
3) The relationship to the exposure triangle is how the aperture and the shutter speed work together.