Focal plane

Longitudinal sections

In optics, spherical aberration is an image imperfection that occurs due to the increased refraction of light rays that occurs when rays strike a lens or mirror near its edge, in comparison with those that strike nearer the center. It is often considered to be an imperfection of telescopes and other instruments which makes their focusing less than ideal due to the spherical shape of lenses and mirrors. This is an important effect, as spherical shapes are much easier to produce than aspherical and so most lenses have spherical shapes. Image File history File links Download high resolution version (1292x774, 291 KB)A simulation of spherical aberration in an optical system with a circular, unobstructed aperture admitting a monochromatic point source. ... Image File history File links Download high resolution version (1292x774, 291 KB)A simulation of spherical aberration in an optical system with a circular, unobstructed aperture admitting a monochromatic point source. ... Image File history File links Download high resolution version (1024x1542, 199 KB)A simulation of spherical aberration in an optical system with a circular, unobstructed aperture admitting a monochromatic point source. ... Image File history File links Download high resolution version (1024x1542, 199 KB)A simulation of spherical aberration in an optical system with a circular, unobstructed aperture admitting a monochromatic point source. ... See also: List of optical topics Optics (appearance or look in ancient Greek) is a branch of physics that describes the behavior and properties of light and the interaction of light with matter. ... // Headline text This article refers to refraction in waves. ... A lens. ... A mirror is a surface with good specular reflection that is smooth enough to form an image. ... 50 cm refracting telescope at Nice Observatory. ... Look up focus in Wiktionary, the free dictionary. ... A sphere is a perfectly symmetrical geometrical object. ...

The effect is proportional to the fourth power of the diameter and inversely proportional to the third power of the focal length, so it is much more pronounced at short focal ratios, i.e., "fast" lenses. A 35mm lens set to f/11, as indicated by the white dot above the f-stop scale on the aperture ring In photography the f-number (focal ratio) expresses the diameter of the diaphragm aperture in terms of the effective focal length of the lens. ...

For small telescopes using spherical mirrors with focal ratios shorter than f/10, light from a distant point source (such as a star) is not all focused at the same point. Particularly, light striking the inner part of the mirror focuses further from the mirror than light striking the outer part. As a result the image cannot be focused as sharply as if the aberration were not present. Because of spherical aberration, telescopes shorter than f/10 are usually made with non-spherical mirrors or with correcting lenses. A 35mm lens set to f/11, as indicated by the white dot above the f-stop scale on the aperture ring In photography the f-number (focal ratio) expresses the diameter of the diaphragm aperture in terms of the effective focal length of the lens. ... The Pleiades star cluster A star is a massive body of plasma in outer space that is currently producing or has produced energy through nuclear fusion. ...

In lens systems, the effect can be minimized using special combinations of convex and concave lenses, as well as using aspheric lenses. Convex lens converging light rays A convex lens is a lens that is curved outward (convex): the ends are narrow and the middle is wide. ... concave lens diverging light rays A concave lens is a lens with inward-curving (concave) surfaces: the ends are wide, the middle is thin. ... An aspheric lens or asphere is a lens whose surfaces have a profile that is neither a portion of a sphere nor of a circular cylinder. ...

See also

• Aberration in optical systems
• Maksutov telescope
• Parabolic reflector
• Ritchey-Chrétien telescope
• Schmidt corrector plate