@Suhail78 and anyone interested...
ND filters ie Neutral Density filters allows you to reduce the amount of light getting to your camera's sensor. I use the tern Neutral loosely as you will find that some cheaper ND filters aren't 100% neutral gray but have a tint to them that show up as a colour cast/bias in your video. Are they needed? Yes and no.
If you just want to fly around and shoot basic video and don't care about smooth looking pans etc, save your money.
If you want that smooth looking pan/trucking shots or smooth movement on moving subjects, you will need to shoot at 24fps and roughly double your set FPS which means you need to bring your shutter down to 1/50" or 1/60".
In order to do so, you need to counteract reducing light by decreasing the aperture size or sensitivity ie ISO setting by the same amount. Unfortunately the aperature setting on the drone's camera is fixed at f2.8 so your only other option is to drop ISO down by the required stops of light. Here's the second limitation, your drone can only drop to ISO100 so with your hand tied with a fixed f-stop and minimum ISO100, the only option in order to reduce the amount of light down so that your image is properly exposed at 1/50" or 1/60" is by means of a ND filter.
Not all ND filters are created equal. As I mentioned earlier above, not all ND filters and 100% neutral gray. The cheaper ones tend to have a magenta bias to in the video. This you can correct for the most part in post production. Better quality filters are usually more expensive because they are more neutral with very little (if any) colour bias and also have multi-coated glass.
The multi-coating on the filters helps reduce flares which can be a good/bad thing. If you want to get that solar flare look, try with a non-coated filter and shoot anywhere from 0-45 degrees towards the sun.
Then we have ND Polarized filters which helps reduce reflection/glare on foliage, water and other reflective surfaces, sky etc. Think beaches, lakes, ponds, lush vegetation areas. The drawback to ND PL filters is that the wide angle of your drone's lens is beyond the max coverage area of your filter. Keep in mind that a polarizer is stongest 90 degrees to the sun. Therefore at certain directions away from the sun, you will find uneven colouration in the sky ie dark in one part and much lighter in another part of your video. Use wisely ie limit the amount of sky in your framing or keep the video moving etc.
ND8 is good for early morning, late afternoon shooting. ND16 is good for mid-morning and mid-afternoon. ND32 is good for between mid-morning to mid-afternoon.
One added bonus to shooting 24fps @ 1/50-1/60" is that your drone's props won't be easily visible because it's spinning faster than the slow shutter speed can pickup.
I've had good luck with the Polar Pro Cinema Series ND/PL filters but would like other's inputs on other quality brands to look out for.
If you need to increase shutter speed for stills, the quickest way without bringing the drone down is to up the ISO to 200 or 400. That should give you 2-stops faster shutter speed.
