In a telephoto lens, the magnification of the subject is achieved through a combination of convex and concave lenses. In its simplest form, a convex lens on the outside converges light.

Lenses are used in cameras, telescopes, binoculars, microscopes and corrective glasses. A lens can be converging (convex) or diverging (concave).

A telescope's power, or magnification, has to do with its lenses. Magnification is determined by the focal length of the telescope divided by the focal length of the eyepiece.

Galileo's device was a 20-magnification instrument that used a convex objective lens and a concave ocular lens. This design was the only real workable telescope of the day.

Galileo's contemporary Johannes Kepler, a German mathematician, discovered a way to get beyond the magnification ceiling. Instead of a concave lens near the eye, Kepler used a convex lens.

Galileo's contemporary Johannes Kepler, a German mathematician, discovered a way to get beyond the magnification ceiling. Instead of a concave lens near the eye, Kepler used a convex lens.

Lens is a piece of transparent glass bound by two spherical surfaces, used to magnify objects. It is an important instrument used in camera, microscopes etc.

Astronomers have constructed telescopes of every kind - massive observatories designed to pick up faint traces of light across space.