What are some of the good brand of ND filters? I've heard of Schneider and Tifen? Which which is better? I'm looking for .3, .6, .9 and graduated ND filters. I know that my EX1 has a built-in ND filters...but I just noticed that ND1 is (I believed) 3 f-stop and ND2 is 6 f-stop on the camera. I don't want to add that much each time. So that's why I'm looking into adding as much as I needed only instead of 3 f-stop each time.