achromatische

Achromatical or achromatisch is an adjective used in several contexts to denote absence of color or color neutrality. In English, achromatic means colorless or without hue, and in optics the term is most commonly applied to devices designed to minimize chromatic aberration in imaging systems.

In optics, an achromatic lens or achromat is engineered to reduce the variation of focal length with wavelength, thereby limiting chromatic aberration. This is typically achieved by combining two or more optical glasses with different dispersion properties, usually a crown glass and a flint glass, into a single lens assembly. By balancing the refractive powers for at least two wavelengths—often red and blue—the focal planes for those wavelengths coincide more closely, improving sharpness and color fidelity. Axial (longitudinal) chromatic aberration is mainly addressed, although higher‑order and lateral chromatic errors can remain. More advanced designs, such as achromatic triplets or multi‑element apochromats, extend correction to additional wavelengths.

Historically, the concept emerged in the 18th century, with Chester Moor Hall credited for constructing the first practical achromatic doublet in the 1730s and Peter Dollond contributing refinements. Achromatic correcting elements became standard in refracting telescopes, cinematography and camera lenses, and microscopy, helping to produce clearer, more accurate images than single-glass lenses.

In design and color theory, achromatic also describes neutral color schemes—black, white, and grays—that lack hue and are used to emphasize form, light, and texture rather than color.

Overall, achromatism represents a foundational approach to improving optical performance by managing wavelength-dependent dispersion.