anyone have a good explanation of ISO? i am just starting to get into all this, but it seems when the iso is higher, the pictures are more grainy... i went shooting today and when i got home i was dissapointed with the results, and the iso was set to like 1280 or something. i turned it down to 400 or maybe 200 i dont remember and took some more pictures and they came out really clear. when and why would you want high ISO?