Check out the filters at -http://freewellgear.com
We did a flight test without the variable ND filter, then with the FREEWELL Variable ND 2-400.
You can notice the increase in the image sharpness and quality, makes a huge difference in post production, a definite must have for your kit guys, a great 10 in 1 filter.
This filter also works for the new DJI OSMO!!!