An achromatic lens, often called an achromat, is a type of optical lens capable of correcting chromatic aberration, a distortion that occurs when glass splits white light into multiple colorwavelengths in the spectrum.

Chromatic aberration is a common type of imaging defect. When white light passes through a singlet lens, the wavelengths of light are refracted. Because different wavelengths pass through the glass at different rates, they come into focus at different points on the plane. As a result, the operator will not be able to bring all the colors into focus simultaneously. Chromatic aberration creates blurry fringes of color between dark and light parts of an image, significantly reducing image quality.

To deal with the problem of chromatic aberration, people rely on achromatic lenses, which combine two or more lenses to direct two wavelengths of light, usually red and blue, to the same focal point.

Though lenses have continued to improve in quality, the achromatic lens remains a staple in scientific and non-scientific optics applications. Some benefits of achromatic lens assemblies include:

Improved image quality: By eliminating color fringes, achromatic lenses significantly increase image brightness and clarity. This fact is particularly true for polychromatic imaging.

Efficient light transmission: Unlike singlet lenses, the on-axis performance of an achromatic lens won’t degrade as aperture size increases, allowing you to utilize the entire clear aperture.

Cost-effective production: Though improvements on the achromat exist, these lenses are much more expensive. For most purposes, an achromatic lens provides plenty of correction, making it the most cost-effective way to get clear white light images.