Greetings everyone, I have a question about the Phantom 3 pro's camera that I can't find information on and maybe I can get that here.  I'm a CG artist that specializes in architectural renderings and animations, I bought the drone in the hopes that I could use it in my work.  If you’re interested in the kind of work I'm looking to do with the Phantom watch the video below, basically I'm going to composite 3d models onto a background plate that I'll shoot with the drone.  In order to do that I have to run the footage through a program that re-creates the camera's position and then bring that information into a 3d modeling program.  All of that has been successful however there seems to be a discrepancy between the camera lens the software predicts and the actual lens on the drone.  I know the camera lens has a 94 degree FOV but the software keeps saying it's about a 75 degree FOV, I think this may be due to the distortion of the lens but I'm not sure because I can't find any info on the lens.  The software estimates the lens of the camera at 13mm, I'm not sure if this is correct, can anyone tell me what it is?  Thanks for your help.


password: big tree

You can check the specs of the camera here. http://www.dji.com/product/phantom-3-pro/info#specs

The focal length of the lens is 3.61mm, but (with apologies if this is obvious), the sensor on the camera is a "1/2.3-inch" sensor, which measures 6.17mm x 4.55mm.  Since the standard 35mm frame is 36mm x 24mm, the P3 has a crop factor between 5.27 and 5.83, meaning that its lens gives the same FOV as a 19-21mm lens on a standard 35mm camera.

(The ambiguity is because they have different aspect ratios:  35mm film has a 3:2 aspect ratio, while the P3P has a 4:3 aspect ratio.  The convention is to define the crop factor as the ratio of diagonals, which is 5.64, and implies that the lens is equivalent to a 20.3mm.  But this is kind of an apples-to-oranges comparison; in a lot of cases the horizontal FOV is more important, in which case the lens behaves more like a 21mm lens.  Not a big difference between 20.3 and 21, though.)

Anyway, the lens does have a fair bit of [barrel] distortion, and it's possible that if you were to extrapolate from the behavior in the very center of the image, you'd infer a diagonal FOV of 75 degrees.  But the actual FOV is pretty close that of a 20mm lens (or, to be more precise, to the FOV of my 10-22mm lens, set to 12.5mm, on my Canon APS-C camera), which is 94 degrees diagonally.  However, the horizontal and vertical FOV are only 81 and 64 degrees (respectively).

I guess the real takeaway from all this is that there are a lot of numbers running around, and it's hard to say exactly what your software is getting confused about.  If I had to guess, maybe it cares about horizontal FOV (which should be about 80 degrees), and is getting faked out by the barrel distortion, and thus concluding that the P3 camera has a 75 degree horizontal FOV?

I don't know what the 13mm is doing in there, since there's no way in heck the P3 camera is anywhere close to the FOV of a 13mm lens on standard 35mm film.  Unless you've been using (and your software is therefore assuming) an APS-C camera, like a Canon EOS 7D or 70D, or the Nikon equivalent?  A 13mm lens on APS-C (1.6x crop factor) has a FOV that's very similar to that of the P3 camera.

Final note:  architecture is (notoriously) a field where distortion is your enemy.  Architectural photographers routinely drop a few grand for Canon's TS-E lenses to minimize distortion.  Moreover, if you're going to use a drone for your work, then you absolutely have to get a private pilot's license (or hire one) in addition to getting a Section 333 exemption -- otherwise the FAA will come down on you like a ton of bricks as soon as you bill a client.  Given that you're looking at spending around $10K (cost of a pilot's license) to use any drone in your work... why not plan on spending a few $K extra for a larger drone that can hoist a real camera, with a pro lens?  The P3 is amazing at what it does, but the camera isn't up to architectural standards.