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 ?
The shape of the secondary reflector should be directly related to the primary concentrator (the achromatic lens) because it works on the previously deflected rays.
Along this section, following the Fermat's principle (Snell equations), an innovative Fresnel achromatic doublet is proposed (hereafter mentioned as achromatic lens) which forms the core of the following development and simulations in the present paper.
Sporting an achromatic lens of 3.5-inch (90-mm) aperture and a focal length of 1,000 mm (f/11), this refractor delivers powers of 111x and 40x with the supplied 9-mm and 25-mm eyepieces.
Featuring a multicoated 4.7-inch (120-mm) achromatic lens with a 1,000-mm (f/8.5) focal length, this refractor is supplied with an EQ-3 German equatorial mount with dual-axis slow-motion controls (motor drive extra), setting circles, a built-in polar-alignment scope, and an aluminum tripod.
This 4.7-inch (120-mm) Newtonian reflector employs a multicoated negative achromatic lens to provide an effective focal length of 805 mm (f/6.7) in a short tube.
The ingenious British optician Horace Dall designed a novel form of two-element achromatic lens to compensate for atmospheric dispersion.
Since the second achromatic lens is mounted inside the eyepiece tube and the light rays have been made parallel by the first lens, the eyepiece's focus remains unaffected by this adjustment.
His first telescope combined an achromatic lens of 14-inch focal length with an eyepiece scrounged from an old pair of binoculars.
Instead, we formed the image with a 6-mm achromatic lens of 200-mm focal length and reduced its brightness with a neutral-density filter.