FPV Camera Field of View (FOV)
The majority of these little FPV cameras will come standard with a 3.6mm focal length lens giving about a 90 degree FOV which is a nice all round field of view for FPV. The lower the focal length number, the wider the FOV (sees more of the environment but fish eye starts appearing). The higher the focal length number the more zoomed in the image will appear. Again, stick with 3.6 mm or about a 90 degree field of view for your first FPV camera and you will have good success.
These little 12mm lenses don’t cost much (about $10 bucks) so it’s not expensive to experiment later on if you choose one of these FPV cameras with changeable lenses.