First time I have experienced this, after a 30 mile scooter ride in 9 degree cloudy conditions arriving at my destination I noticed that my OA3's lens was misted up internally. The moisture was to the bottom left of the central part of the lens cover (not the actual lens itself) & unfortunately I didn't take a picture of it on my phone.
The lens cover had never been removed before, I unscrewed it and wafted it at arms length until the condensation cleared, put it back on and was good to go.
The only difference with this journey was that it was the first time I used my new foam wind shield.
In the picture the bottom left corner is effected. Luckily it wasn't enough to spoil my video.

What could have caused this and how to stop it in future?

when home re-open and  place in an open areal and let air dry out.  was the lens protector easy to untwist or snug and tight?   

FISH

Thanks Fish, good idea. It was a very snug fit & hard to remove as I don't have the rubber ring on it.

FYI water can enter a loose lens cover. and get to the sensor, ask me Lol happ'd to me but never fogged up on teh outer lenses

What does a foam windshield look like? What resolution were you filming? Was it 30 miles as in kilometers and 9 degree Celsius as in Fahrenheit? :-) I thought they use metric in the UK, no? 30 miles is about 48 kilometers. If you travel with the speed of, say, 25km/h then it would be about a 2 hour ride. If you film in 4k (for about 2 hours), then maybe the camera got a little warm internally and maybe the foam didn't allow the internal heat to dissipate hence causing condensation.

Of course this is just a weird theory. You might need to ride a few times and test it with and without the foam.

I'm looking at this Puluz high density foam. This seems to surround the lens. Since (according to DJI) the lens cover is used for heat dissipation, and if the foam snugs it like on this photo, then maybe my theory could be right. Or not.

https://www.puluz.com/p/PU405/PU ... tion-with-Frame.htm

Sorry, I forget this forum is worldwide.
Filming resolution was 4K 60, temp was 9 degrees celsius and distance was 30 miles as in 30 UK miles. For the whole journey my satnav recorded 64 miles at an average of 29mph, lots of country roads and only one faster 70mph section. Destination by the way was Stansted Airport viewing area, Essex, UK.
The camera was mounted at the bottom of the windshield - so right out in front and in the full force of the wind.
The foam windshield is not dense as you linked to, it's an open much softer type but it does hug 3/4 around the outer lens. Although the picture was from the product site, it is not dense as shown.

It seems like I fell asleep for I had no idea UK is still using miles.

We can be a stubborn race at times, it's taking us years to adopt the metric weights system. If you're of a certain age, you need to be conversant with both metric and imperial measurements
Luckily we didn't adopt the Euro.

Normally I don't use 4k 60, 50 is my preferred frame rate - so that may have caused a little extra heat. Didn't realise it was set that way.

Hi there. Thanks for reaching out, and we're sorry you encountered such issues. May we confirm if you are using the official Osmo Action 3-Lens Protective Cover? Please note that large temperature differences between the inside and outside layers of the camera lens may cause the lens to fog. Also, humid and low temperatures can affect the lens. You may eliminate the fogging by leaving it in an area at room temperature. In addition, here are some tips you can follow to maintain your lens cover:
1. It is not recommended to attach and detach the lens protective cover frequently, otherwise, dust may accidentally fall into the lens cover, which will affect the shooting quality. When the masking paper within the protective cover is dusted, it is not easy to clean up due to the structural design of the cover, so it is not recommended that you remove and attach it frequently.
2. After recording and shooting for a long period, do not touch the lens protective cover, to avoid burns. If disassembly is required, please power off the camera and wait for the camera to cool down completely before operating.
3. Do not open the lens protective cover immediately after the camera is taken out of the water. Otherwise, water vapor may enter the cover, and thereby leading to fogging inside the lens cover. Wipe to clean and dry the camera in advance if disassembly is necessary.
4. Do not remove the lens protective cover in a place with large dust.
5. If you feel that the lens cover is difficult to remove, it is recommended to remove and attach it with the rubber lens protector installed.
Should you have other inquiries, please reach back here at DJI Forum. Have a nice day.

Hi DJI Tony,
Yes I can confirm I was using the official Osmo Action 3 lens cover, as I stated in my original post, the lens cover had never been removed.
Thanks for all your information, noted.
Never had any issues before even when used in colder conditions. The one thing I will say is that when last used the camera battery and card were removed and so battery door was left open overnight.

m326 Posted at 2-15 05:45
Hi DJI Tony,
Yes I can confirm I was using the official Osmo Action 3 lens cover, as I stated in my original post, the lens cover had never been removed.
Thanks for all your information, noted.

We understand. We recommend you continue to monitor your product and feel free to use it. Happy filming!