I have 2 ND filters: an ND8 for bright sunny days, and an ND4 for hazy, thin overcast days. Haven't had them that long, but so far, they make my aerial videos look SO much better, especially the ND8, since I like to shoot on bright clear days.
When the naked camera is installed in the gimbal and the two small included weights are added to the top & bottom, as specified, the camera stays where you put it, which is what a powered-off gimbal is supposed to do. Regardless of the position of the camera, a perfectly balanced gimbal will not move at all, so when powered on, it's not fighting to keep it level, which would put added strain on the motors.
I have a Hero 4 Silver, and purchased my two BlurFix Air filters for it because they're very light. But "very light" does not equal no weight at all. So of course the filter causes the camera to fall forward and to the left (when standing behind the camera), since the lens & filter are on the front left side.
So the goal was to find the amount of weight, and the correct position, to add weight to the rear and right side to offset both off-level situations (fore-and-aft & side-to-side).
I tried several different combinations of coins to see what worked, attaching them lightly with Scotch tape to test. If either side, or front or rear of the camera fall, the motor has to work to make up the difference. I came pretty close with combinations of pennies and dimes. But when I was pretty close, but not quite there, firing up the gimbal would result in an audible motor noise coming from it, letting me know that it was fighting to stay level, instead of falling there naturally.
I finally found the closest weight and position, that resulted in almost-perfect level in all directions, and no motor noise whatsoever: a nickel on the rear and a nickel on the right side (again, standing behind the camera).
I attached a small square of industrial-strength velcro (available on Amazon:
http://bit.ly/velcro-1-inch-industrial-strength) to the rear and right side, and the opposing piece to the nickels (cut perfectly round to fit).
I've flown about 9 batteries since setting this up, regularly checking the balance of the un-powered camera/gimbal and for any sign of motor noise when powered up. So far, so good, with great, smooth flights, and no sign that I'm stressing the gimbal motors.
Attached photos show the exact placement of velcro and coins. Again, this is for a Hero 4 Silver. Might be different for other models. If anyone has tried anything else that works well too, please share! The difference in quality with an ND filter is too good to omit just because 3DR didn't make weights for them.
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