A thin lens, made of flexible or rigid plastic, that is placed directly on to the eye to correct vision, used as an alternative to spectacles, or, if coloured, to change one's eye color cosmetically.

(physics) a magnetic field with axial symmetry capable of converging a beam of charged particles of uniform velocity and of forming images of objects placed in the path of such beam

(astronomy) A massive body that produces distorted, magnified or multiple images of more distant objects when its gravitational field bends the path of light rays.

A stray patch of brightness in a photographic image resulting from aberrant refractions or reflections within the lens due to an exceptionally bright light source, sometimes one just outside the image proper.

(photography) A lens that allows a camera to focus at very close range to photograph small objects.

(optics) A lens having at least one convex surface, such that light passing through it may be brought to a focus.

The hollow cylindrical lens used in the Fresnel lantern.

A microscopic objective of short focal distance designed to work with a drop of liquid between the front lens and the slide, so that this lens is practically immersed.

A large lens constructed in several parts or layers, extending in a series of annular rings beyond the central lens, and used in lighthouses.

(microscopy) A condensing lens in which the light is confined to an annular pencil by means of a small, round diaphragm (the "spot"), and used in darkfield illumination.