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
A refractor lens, made of two or sometimes three separate lenses, which has the effect of bringing most of the viewed colours to a sharp focus, thus reducing chromatic aberration Finder Scope: A low power telescope attached parallel to the main instrument which provides easy object locating and telescope aiming
An Achromatic lens is a system of lenses joined in order to minimize color and shape distortions (chromatic and spherical aberrations) that are inherent in a single lens system
Refers to a lens which has been partly corrected for chromatic aberration Such a lens is customarily made to bring green and red light rays to approximately the same point focus Also called an achromat