The most common type of objective lens found in a refractor telescope. An achromat has two elements made of two different types of glass with different refractive indicies. A properly designed achromat will bring at least two different wavelengths (colors) of light to a common focus. In practice, achromats are designed to minimize errors across all wavelengths.

Traditional refracting (lens-based) telescope with two glass elements. False color ( chromatic aberration) is reduced to acceptable levels for smaller scopes. Also see apochromat, refractor, chromatic aberration.

A lens made of two pieces of glass (or, occasionally, other materials) with differing optical properties, specifically chosen to minimize chromatic aberration (which see).

a positive simple lens cemented to a negative simple lens

A refractor or lens element that is optimized to reduce chromatic aberration to a minimum.

A lens which is corrected for operation at different wavelengths of light, and is hence achromatic. This is usually achieved by using more than 1 optical element.

A lens doubled, to two lenses combined to eliminate chromatic aberration.

A lens made with 2 or more elements which tends to prevent chromatic aberration. A lens made with two glass elements which lessens chromatic (color separation) aberrations.

A 2-element telescope eyepiece designed to remove the false colours caused by chromatic aberration.

A high-quality objective lens that display very little prismatic color.

An objective lens system constructed of glass with limited quality of correction for color and spherical aberration.