The lens on the stock camera distorts the picture and you loose focus around the edges. This can be fixed by purchasing an inexpensive replacement lens (less than £10). This is an example lens that you can buy to replace the stock one.
For instructions on how to change the lens watch the below youtube video;
I used the stock camera for flying FPV, when I want to take better quality video I swap it out for a GoPro or Apeman camera.