It seems that a few of the reviewers recommend not using ND filters while filming in HDR. But yesterday when I'm trying to film a new roof on an industrial building that have a flat whie top coat. I was still seeing over exposured area on the screen and you can not see as much surface detail at certain angle when I watch the shot afterwards. Would using a ND filter helps? Or should I use a polarizer?

A neutral density filter is just that - neutral. It should have no effect on the colour or dynamic range of the image. They are used to slow the shutter speed without over exposing the image in various levels of light and thus to provide more control over the motion blur when recording video - HDR or otherwise. Polarisers will simply make the blues and greens pop more and cut through glare such as large surfaces of water providing it is in line with the right direction of the sun.

You will find that in a wide angle frame the drone will draw a median value of exposure across the whole image - so some parts may be slightly over exposed whilst other areas of the image are underexposed in order for the overall image to be correctly exposed.

An ND filter will simply darken the overall image and are not used specifically for controlling exposure value. You'll be better off controlling the exposure with the shutter speed and the angle the camera is in line with the sun. If you want control over motion blur and to decrease your shutter speed closer to the frame rate (double is best) then you'll need ND filters for that purpose. You do not need polarisers for recording roof tops unless the roof tops are made of glass and you are flying in a straight line!

Thanks Aj for the information. Do you know what the numbers on these filters mean?

My answer is "hell, no". In my experience, when using HDR the MA2 is trying to correctly expose for the darker areas by dropping the shutter speed. Dropping it way down, to 1/30 and generating an unusable amount of motion blur. The last thing you want to do is to help that process along by adding an ND filter. Keep in mind ND filters do not affect the way your image looks, you can't fix stuff you don't like in your image (like overexposed areas) by using an ND, you fix those by playing with the shutter speed and the ISO. NDs are used simply to bring down the shutter speed when it's too high, in order to obtain the cinematic motion blur.
The x in NDx is how many times you'll have to increase your shutter speed to get the same level of exposure with the ND filter on that you had with it off.

Example: getting correct exposure for a particular scene with no filter at ISO 100 and SS 1/640. Adding an ND8 means, in order to keep the image looking just as before, you need to go with ISO 100 and SS 1/80.

OK, Thanks all

JCEsp Posted at 8-12 13:16
Thanks Aj for the information. Do you know what the numbers on these filters mean?

The amount of F-stops the filter has to prevent light from hitting the sensor. The higher the F-stop the less light will hit the sensor.  

Wiz33 Posted at 8-12 14:11
OK, Thanks all

You're welcome  

JCEsp Posted at 8-12 13:16
Thanks Aj for the information. Do you know what the numbers on these filters mean?

Do you know what the numbers on these filters mean?
They indicate how much light the cut.
eg ..An ND8 filter only lets 1/8th of the light through
An ND16 filter cuts 94% of the light and only lets 1/16th get through.

You'd do better to try shooting from a different angle or shooting in overcast conditions.

Hi. Thank you for reaching out to DJI Forum. With regards to this inquiry. I hope that our valued DJI co pilots can provide you the best recommendation for this query. Thank you.