Brilliant, a thread with a particular issue I am having... I need a square filter ND, 6 stops, to stack together with the Big Stopper to get 16 stops... Neuro any idea? Lee make 3 stop NDs, but I guess stacking a 10 stop Big Stopper and two 3 stop NDs would be overkill in terms of vignetting. Hitech, Cokin or BW make a 6 stop 100 mm square filter anyone knows?
I've got some tests with several ND filters (LCW Fader ND, Tiffen screw-ins, cheap resin filters) over here:http://www.similaar.com/foto/lenstests/lenstestsn.htmlMy conclusions:* sharpness is not an issue, even on a D800, as long as you use decent filters (no fader, no cheap resin)* color cast is an issue, but it's relatively easy to fix (at least with my filters)* stacking filters is not as bad as people think