<P> A curved mirror is a mirror with a curved reflecting surface . The surface may be either convex (bulging outward) or concave (bulging inward). Most curved mirrors have surfaces that are shaped like part of a sphere, but other shapes are sometimes used in optical devices . The most common non-spherical type are parabolic reflectors, found in optical devices such as reflecting telescopes that need to image distant objects, since spherical mirror systems, like spherical lenses, suffer from spherical aberration . One advantage that mirror optics have over lens optics is that mirrors do not introduce chromatic aberration . </P> <P> A convex mirror, diverging mirror, or fish eye mirror is a curved mirror in which the reflective surface bulges toward the light source . Convex mirrors reflect light outwards, therefore they are not used to focus light . Such mirrors always form a virtual image, since the focal point (F) and the centre of curvature (2F) are both imaginary points "inside" the mirror, that cannot be reached . As a result, images formed by these mirrors cannot be projected on a screen, since the image is inside the mirror . The image is smaller than the object, but gets larger as the object approaches the mirror . </P> <P> A collimated (parallel) beam of light diverges (spreads out) after reflection from a convex mirror, since the normal to the surface differs with each spot on the mirror . </P>

When is the concave surface of the mirror used