Definitions for "Apochromat"
A type of compound lens that uses either three or more elements, or special glasses, like fluorite or ED glass, to bring at least three colors to a common focus. In practice, errors are minimized across all wavelengths in order to achieve a very high degree of color correction. Most camera lenses are apochromatic. Compare this with an achromat.
A special construction which reduces or corrects erroneous colours.
High-quality refracting (lens-based) telescope with expensive and exotic glass element(s). False color (chromatic aberration) is reduced to imperceptible levels. See also achromat, refractor, chromatic aberration. Expensive.