I'd really like to find a good, economical solution to put ND filters in front of my set (75, 50 and 35mm in OCT18). I know that a matte box with 4x5.6 would be the most elegant solution, but I can't justify the cost since I wouldn't be using it use it with my other lenses. I use a fader for those. I have contemplated trying to trap a large-diameter ND fader in a lens collar (mounted to a rail block) and then sliding that in front of my lenses. But that seems like a disaster waiting to happen. Surely there must be a better solution. Anyone have any ideas?