anastigmat

The term anastigmat refers to optics that minimizes three common aberrations: astigmatism, coma, and spherical aberration. The term is used for a lens with such capability which is also called an anastigmatic lens. Such lenses generally consist of multiple individual lenses, each of which may employ multiple layers of refracting material. They are often used in quality cameras, binoculars, and refracting telescopes. The term is also used to describe reflector telescopes with features to carry out the same goals, e.g., a three-mirror anastigmat telescope, with three successive mirrors of different shapes to do so, an example being the James Webb Space Telescope.