I was extremely excited about the ND Fader, a variable neutral density fader that attaches to the front of the lens, because it offered an alternative using the iris or shutter speed to control the light / exposure. As we know shutter speed effects the blur or lack there of. Films have traditionally been shot at twice the frame rate, i.e. 1/48 sec if using 24 fps, giving a smooth look to the motion. This is what we are used to seeing and may seem like a natural look. Some movies and music videos, however, looking for a different look shoot at faster shutter speeds.
To achieve the desired shutter speed while maintaining a certain aperture speed (and iso) we use ND filters. Normally video cameras have these built in and film cameras use a matte box with slots for interchangeable filters. I don't yet have a matte box and am putting off getting one until I have to. So I have gone with the cheaper option - screw on nd filters. You can get various fixed ND filter i.e. 2,4,8 or you can get a variable ND fader that works like a circular polarizer - rotate to increase or decrease effect.
I bought my ND Fader from trademe.co.nz and it isn't the genuine article from france but a cheap Chinese knock-off which is always a risky road to travel but also kinda adds to the excitement. So here I have done some very basic comparisons of video shot at 1/50th, 1/100th, and 1/500 of a second, (using an ND Fader to control the light).
The tests were done on a Canon 5D mk2 with a Canon 24-105mm L lens at f/4 and 25fps.
Note the difference in motion, colour temp, saturation, and flare from sun.