An achromatic lens or achromat is a lens that is designed to limit the effects of chromatic and spherical aberration. The most common type of achromat is the achromatic doublet, which is composed of two individual lenses made from glasses with different amounts of dispersion. Usually one element is a concave lens made out of flint glass, which has relatively high dispersion, while the other, convex, element is made of crown glass, which has lower dispersion. The lens elements are mounted next to each other and shaped so that the chromatic aberration of one is counterbalanced by the chromatic aberration of the other, while the positive power of the crown lens element is not quite equaled by the negative power of the flint lens element. Together they form a weak positive lens that will bring two different wavelengths of light to a common focus. Achromatic lenses are corrected to bring two wavelengths (typically red and blue) into focus in the same plane. Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... A lens. ... Chromatic aberration is caused by the dispersion of the lens material, the variation of its refractive index n with the wavelength of light. ... 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. ... A doublet is a type of lens made up of two lenses with different refractive indices attached together. ... Glass can be made transparent and flat, or into other shapes and colors as shown in this sphere from the Verrerie of Brehat in Brittany. ... Dispersion of a light beam in a prism. ... concave lens diverging light rays A concave lens is a lens with inward-curving (concave) surfaces: the ends are wide, the middle is thin. ... Flint glass is an optical glass that has relatively high refractive index and low Abbe number. ... Convex lens converging light rays A convex lens, or converging lens, is a lens that is curved outward (convex): the ends are narrow and the middle is wide. ... Crown glass is a type of optical glass used in lenses. ... Optical power or dioptric power or refractive power is the degree to which a lens or mirror converges or diverges light. ... The wavelength is the distance between repeating units of a wave pattern. ... An image that is partially in focus, but mostly out of focus in varying degrees. ...
The first achromatic refracting lens was invented in 1733 by an English barrister named Chester Moore Hall although it was independently invented and patented by John Dollond. This article or section does not adequately cite its references or sources. ... Chester Moore Hall (1703–1771) was a British lawyer who produced the first achromatic lenses in 1729 or 1733 (accounts differ). ... John Dollond (June 10, 1706 - November 30, 1761) was an English optician. ...
achromatic correction of light in the visible region is conducted by correcting said axial chromatic aberrations with a diffracting function of said diffractionlens.
The achromaticlens system according to claim 3, wherein the second positive lens element of said front lens group is cemented to said negative lens element of said front lens group.
In the lens system according to the present invention, the frontmost and rearmost surfaces of the front lens group 11 on the object side and the image side are respectively made of a convex surface and a concave surface.
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