The focal length of the mirror is simply the distance between and . As is easily demonstrated, in the paraxial approximation, the focal length of a convex mirror is half of its radius of curvature. There are, again, two alternative methods of locating the image formed by a convex mirror. The first is graphical, and the second analytical. An incident ray which is parallel to the principal axis is reflected as if it came from the virtual focus of the mirror.