Light approaching a concave mirror parallel to a radius directed toward the center of the mirror is reflected back and converges at the focal point. How the image appears in its reflection depends on its position relative to the focal point. If the object is behind the focal point, the reflected image is a real image that appears upside down. If the object is between the focal point and the mirror, the reflected image is a virtual image that appears rightside up. If the object is at the focal point, the reflected image
disappears. The reason for the absence of a reflected image in this last case is that the light rays reflected from the object toward the mirror are in turn reflected from the mirror parallel to each other. Thus the rays never converge and an image is never formed.
