Tuesday, February 25, 2014
Get Above It All, Part II
This is the second in a series of articles on aerial imaging using drones. In this issue, we look at gimbals, FPV and aerial imaging techniques.
Once your aerial imaging platform is set up for FPV and vibration-free image capture, you're ready to begin to optimize the images captured by your flying camera. One reminder about aerial imaging is that piloting skill is absolutely the most important variable in the equation. This will likely change in the future, as aerial platforms focus more and more on autonomy and safety, but in the near future, your images are only going to be as good as your piloting skills are. Practice safely, and practice often.
Capturing still images using a GoPro on a Phantom is straightforward, since there aren't very many options you can set. I commonly use my GoPro HERO3 Black Edition in time-lapse mode at 2-second intervals. This gives me hundreds of pictures per flight, but storage is cheap, and I'm happy to throw away most of the images that are captured, keeping only the best. The other reason 2 seconds is the magic number is that the GoPro won't output real-time video when it's shooting at 0.5- or 1-second intervals. Shoot any faster than 2-second intervals, and FPV goes dark.
Getting good exposures from an aerial GoPro can be tricky at certain times of day. Shooting midday in bright, sunny conditions doesn't usually pose a problem, but if it's cloudy, the dynamic range necessary to capture both sky and ground is too large for GoPros (and most cameras on the market). In this case, angle your camera down to get the camera to expose for the ground. You'll blow out the sky, but your subject is most likely terrestrial, and you'll probably want to optimize for that.
New quadcopters like the Phantom 2 Vision have integrated cameras, which allow for camera control during flight. The well-designed iOS app for the Vision lets users switch between still and video modes, start and stop the camera, set exposure, and more. It's a little awkward to have to remove one's hands from the sticks in order to adjust the camera and take a picture, but one can either have a second person control the camera or set the camera to video/time-lapse mode and focus on flying. Note that the Phantom 2 Vision's gimbal is pitch-only and uses a servo. This effectively makes it a composition tool (camera angle up and down) and not a stabilization tool.
In the previous article in this series, I recommended shooting video at 60p (frames per second) to minimize jello. However, if you've balanced your props and are using properly tuned vibration isolation to mount your gimbal, you should have no jello in your video, even at 24p. It's important to note that some tuning still may be required even in ready-to-fly solutions. Almost all gimbal manufacturers ship gimbals with multiple vibration isolators, suggesting that there's no catch-all solution to eliminating jello. In my case, I had to swap out the silicone balls in my Zenmuse H3-2D gimbal with softer ones (included) before jello disappeared from my setup, even though my propellers are perfectly balanced.
In my aerial video pursuits, I typically set my GoPro for Protune with manual white balance in one of the following video modes: 2.7k/30p Wide, 1080/60p Wide or 1080/30p Medium. I like the less-distorted look of Medium FOV, but shooting in 2.7k is flexible because I can crop and still have plenty of data to output 1080p. I shoot at 60p when I want to slow down footage a lot in post, but even at 30p, you can slow footage down to 24p, which is a pleasing effect.
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