When the DJI FPV system first released, there was basically only one choice to make: which vTX do you want? The full sized Air Unit or the smaller Vista. Now, the situation has gotten more confusing. DJI has handed off distribution of the FPV system to Caddx and Runcam, meaning there are more products to decide between. But the decision isn’t actually as complicated as it seems.
First thing to keep in mind is that the video transmitters (vTX) are all identical. Whether you buy a Caddx Air Unit Lite or a Runcam Link vTX doesn’t matter. They’re completely identical in every way, and we even suspect (but can’t prove) that the vTX are manufactured by DJI and just re-labeled as Caddx or Runcam. The cameras, on the other hand, are manufactured by Caddx and Runcam, and are not the same.
First, you have to choose which vTX you want. There are two choices: the full sized Air Unit (Caddx calls this the Air Unit Micro), with two antennas and an SD Card slot, or the smaller Air Unit Lite (previously known as the Caddx Vista vTX). The Air Unit Lite saves about 20 grams compared to the Air Unit and doesn’t have a built in DVR. It has 20mm mounting holes and will fit in the rear of most 5″ freestyle frames, as well as many smaller frames. For a typical freestyle build, most pilots prefer the Air Unit Lite. If you strongly prefer to have an on-board DVR, such as if you don’t plan to carry a GoPro, then the full size Air Unit would be your pick. Bear in mind the larger Air Unit requires a larger frame, so the weight difference between the two ends up being more than just the 20 gram difference between the two vTX.
Second, choose a camera. The main distinction between cameras is whether they support 120fps or 60fps refresh rate. The 120fps cameras have lower latency of about 25 to 35 ms, while the 60fps cameras are more like 35-45 ms. Pilots disagree over whether this small difference matters. It depends a lot on the type of flying you do.
Although it’s not directly related to the framerate, 120fps cameras can also adjust image settings like exposure, saturation, and white balance. They can also switch between 4:3 and 16:9 aspect ratio; all of the 60 fps cameras are 16:9 aspect ratio only.
The original DJI camera, the Caddx Nebula Pro, and the camera that is sold with the Caddx Air Unit Micro (which is just a Nebula Pro in a different shaped case) are the only 120fps cameras available for the DJI FPV system today. All others are 60 fps. If you want the lowest latency possible, you’ll need to pick one of these. Fortunately, they also have the best image quality and resolution. Unfortunately, the sensor used in these cameras is more expensive and difficult to get, so they’re often out of stock.
If you’re ok with a 60 fps camera, then you’ll choose based on image quality and size/weight. The Caddx Polar and Runcam Phoenix HD both have worse image quality than the original DJI camera or Nebula Pro, but still acceptable to some. Neither one is clearly superior to the other, and you should compare them in reviews to decide which one you prefer.
For night-time use, the Caddx Polar Micro is the only DJI camera with great low-light sensitivity. It’s a 60 fps camera, but that’s a compromise you’ll have to accept.
If you want the smallest, lightest DJI camera possible (such as for a tootphick-style quad), your choice should be the Caddx Polar Nano. The only other nano-sized camera, the Nebula Nano, has much worse image quality. The Nebula Nano is not unusable per se, but the Polar Nano is much better, and their size/weight is the same.