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.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Abbe numbers are used to calculate the necessary focal lengths of achromatic doublet lenses to minimize chromatic aberration but Abbe numbers do not give real information about the quality of the achromatization.
The achromatic doublet lens is composed of PC in its upper surface and it is completed with PMMA in its lower surface as we show in Figure 3.
The 6-inch objective is an achromatic doublet, as is the 1 5/8-inch finder objective.
These so-called achromatic doublets suffer from an optical defect known as longitudinal chromatic aberration.