Achromatic lens

Achromatic lens refers to a lens that is designed to limit the effects of chromatic and spherical aberration. Achromatic lenses are corrected to bring two wavelengths (typically red and blue) into focus in the same plane.

History

The term "achromatic" means "without color". It has been applied to lens systems that are designed to have much reduced chromatic aberration compared to simple lenses. The first kind of achromatic lens was developed by an English mathematician and astronomer named John Dollond in the mid-18th century.

Design

An achromatic lens can be made by combining two separate lenses, one convex and one concave. The lenses are made from glasses with different amounts of dispersion. Normally, one element is a negative (concave) element made out of flint glass such as lead oxide, while the other is a positive (convex) element made of crown glass. When the two are combined, the chromatic aberration of the one is counterbalanced by that of the other.

Applications

Achromatic lenses are used extensively in microscopes and telescopes, where they help to focus different colors of light in the same plane. They are also used in high-quality photographic lenses, and in applications such as laser systems.

See also

• Chromatic aberration
• Apochromat
• Flint glass
• Crown glass (optics)