achromatic lens


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achromatic lens

(ak-rŏ-mat -ik) (achromat) A two-element lens – a doublet – that greatly reduces chromatic aberration in an optical system. The components, one converging and the other diverging in action, are of different types of glass (i.e. they have different refractive indices); the combination focuses two selected colors, say red and blue, at a common image plane with a small spread in focal length for other colors. The difference in optical power (reciprocal of focal length) for the two colors in one element must cancel that in the other element. By a suitable choice of glasses and surface curvatures, the doublet can be aplanatic as well as achromatic, so that three major aberrations are minimized (see aplanatic system).

Residual color effects in an achromat can be further reduced by using a compound lens of three or more elements – an apochromatic lens; each element has an appropriate shape and dispersive power so that three or more colors can be focused in the same image plane.

achromatic lens

[¦a·krə¦mad·ik ′lenz]
(optics)
A combination of two or more lenses having a focal length that is the same for two quite different wavelengths, thereby removing a major portion of chromatic aberration. Also known as achromat.
References in periodicals archive ?
Hall did not publicize his lens properly, and John Dollond (1706-1761), who prepared an achromatic lens in 1757, often gets the credit.
In an effort to replicate the views he had with Peltier's big refractor (but minus the color aberration inherent in an achromatic lens that size), Doug opted to make his Newtonian's spider with three curved vanes, thus eliminating the diffraction spikes produced by straight-vaned spiders.
5-inch (90-mm) achromatic lens with a focal length of 910 mm (f/10), this refractor is shipped with an altazimuth mount (which has dual-axis slow-motion controls) and an adjustable aluminum tripod.