Flight cams are just small CCTV cameras and are usually 12 Volts but some are 5V, so a converter/regulator may be needed. I use the Adjustable step down regulator, or a Step Up converter, or a 12V BEC (note most BEC’s are 5V). You also might need to add a Torroid filter on the cameras power line near the camera if you have any interference from your main battery/ESC. I sometimes use a separate battery for video and RC all together to eliminate interference and provide redundancy. Wrapping your cameras electronics in aluminum, copper foil or carbon fiber will help too; lil-faraday cage. All Faraday cages and wire shielding should be wired to the battery negative close to the battery.
Some guys use the GoPro as a flight camera with a special plug/adapter, however this is not recommended. The GoPros sometimes shut themselves off or reboot and then you crash. They do make for an awesome HD cam for youtube uploads!
Common flight cams
Lenses, which one to choose for my 1/3” CCD? these can be bought at securitycamera2000.com for just few bucks.
1.78mm = 165º viewing angle, Super Fisheye, widest view. Good for quadrotor, skateboard videos. Has some vignette (black corners).
2.1mm = 150º viewing angle, Semi-Fisheye. Good for quadrotor, not airplanes too wide.
2.8mm = 86º viewing angle. Good for airplane FPV.
3.6mm = 65º viewing angle. Good for airplane FPV.
6.0mm = 50º viewing angle. Only for mounting on a stabilized gimbal, narrow view.
…and so on, the lenses get more telescopic and the more you go the greater they will require stabilization.