I just bought the Nikkor 50mm 1.8 lens for the Nikon D40. When trying to use the aperture ring the camera tells me: "Lock lens aperture ring at minimum aperture (largets f/-number)." I looked in the manual and it says the same thing. Anyone know if there's a way to use the aperture ring on the lens as opposed to the one in the camera? And if not, does anyone know why?