achromatic lens

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A combination of lenses made of different glass, used to produce images free of chromatic aberrations.

Wiktionary

1. n. optics A lens generally composed of two separate lenses, one convex and one concave and generally of different materials, in such a way that the chromatic aberration produced by one is corrected by the other.

GNU Webster's 1913

1. adj. (Opt.) a lens composed usually of two separate lenses, a convex and concave, of substances having different refractive and dispersive powers, as crown and flint glass, with the curvatures so adjusted that the chromatic aberration produced by the one is corrected by other, and light emerges from the compound lens undecomposed.

WordNet 3.0

1. n. a compound lens system that forms an image free from chromatic aberration