EV is basically the exposure. If you're in a dark place, you want to set the number higher. If its brighter you want to set it to a negative number. In neutral conditions, leave it at 0
The ISO is the shutter speed, more or less. In darker conditions (night time, etc) set it to a higher ISO to let in more light. For action shots, set it to a lower ISO.
The only problem with using higher ISOs is that the shutter is open longer so it makes more noise on the picture. So I usually always have mine on 50 or auto.
Bookmarks