I take the usual precautions when flying in cold weather (keep batteries warm, 5 minute cool-down before flight, hovering until battery temperature OK, and an air-tight sack for the Phantom & camera when I come inside), but recently discovered on a few flights that condensation had formed behind my ND filter (a bit like dew inside an underwater camera housing in the tropics). This was particularly noticeable later in the videos with panning scenes. Any tricks to avoid this?

  

You could try a few silica gel crystals in there maybe.  I've never had the filter off so don't know if it's practical.  You may also have some moisture trapped inside, so maybe leave the filter off & surround the camera with silica gel in a box for while.

Or pre-heat the camera with a chemical hand warmer before flight.  Condensation happens when a cold surface contacts with warmer air, so it would only need to be 1 or 2 degrees higher than air temperature.

nigelw Posted at 2016-3-7 21:01
You could try a few silica gel crystals in there maybe.  I've never had the filter off so don't know ...

Thanks Nigel, the silica gel in a box is a good suggestion, perhaps I have picked up some moisture bringing the Phantom home from an earlier flight in the cold...

I haven't had this issue myself but my first thought is to attach the filter somewhere where the aircraft and surrounding air are both cold.

Sincecold air is less able to hold water in suspension than warm air, I'd take a fairly sure bet that this would mean that the air between the camera and lens is less likely to form condensation.

Are they Polar Pro's that you're using? If so they should be fairly air tight......

johnsr Posted at 2016-3-7 21:56
Thanks Nigel, the silica gel in a box is a good suggestion, perhaps I have picked up some moisture ...

You're actually more likely to have picked up moisture from previous warm air; as Anderjon says, warm air carries more moisture.
So, if you put your ND filter on inside your warm humid house, then went outside into the cold, you'll get condensation as the ND glass cools the air trapped between it and the camera lens.

You may find it better to put the filter on outside on a cold dry day and then leave it on all the time.
Ian

Anderjon Posted at 2016-3-8 00:07
I haven't had this issue myself but my first thought is to attach the filter somewhere where the air ...

My filters are DJI ND filters; there is an O-ring, so they should be air tight. As for humidity inside the house, in winter its around 40 to 45% (floor heating, not gas) so shouldn't be the main cause.

wellsi Posted at 2016-3-8 00:15
You're actually more likely to have picked up moisture from previous warm air; as Anderjon says, w ...

Would be a good idea to leave them on, but between flying on sunny days and very cloudy late afternoons it is often necessary to change them. I generally do that indoors before leaving (based upon the lighting outdoors), just to avoid fiddling with these in muddy fields.

Since others don't seem to notice this problem, and under the idea that there is very little air trapped behind the filter, I suspect that Nigel is probably closer to the problem with some humidity trapped inside the camera.