I use a Lee filter system myself with a current total of 6 4"x6" (100cmx150cm) graduated resin filters. I have a pack of 3 neutral density (.3, .6, .9) and there sunset trio of graduated red, orange and yellow. This is all for color transparancy film. For black and white I currently use screw on red, orange, and green. Though I intend to replace them with a 4"x4" resin set (that fits in the above holder) soon.