What does achromatism mean?
Achromatism refers to the property of an optical system — typically a lens or combination of lenses — that is free from chromatic aberration. Ordinary glass bends different wavelengths of light by slightly different amounts, so a simple lens tends to focus red and blue light at different points, producing coloured fringes around images. An achromatic lens, usually made by cementing together elements of crown and flint glass, corrects this defect so that at least two wavelengths come to a common focus; that corrective property is called achromatism. By extension, the word can also describe colourlessness in general — the absence of hue — though this broader use is much less common. The term belongs mainly to the vocabulary of optics, photography, microscopy, and astronomy, appearing in discussions of telescope objectives, camera lenses, and microscope design. Its adjective form, achromatic, is more widely encountered, as in 'achromatic colour' meaning neutral greys, whites, and blacks.
nounThe property of a lens or optical system of being free from chromatic aberration, so that it brings light of different colours to the same focus. More broadly, the state or quality of being without colour; colourlessness.
- In optics: the property of an achromatic lens or system — freedom from chromatic aberration, so that different wavelengths focus at the same point.
- More generally: the state of being colourless or without chroma.
"The telescope's achromatism allowed observers to view Jupiter without the distracting coloured fringes produced by simpler lenses."
"By carefully pairing crown and flint glass, the optician achieved near-perfect achromatism in the microscope objective."
"The room's achromatism — white walls, grey floor, black steel — gave it a stark, gallery-like calm."
Rarely pluralised, since achromatism denotes an abstract property; a plural would appear only when referring to distinct instances or types of achromatic correction.
"Different lens designs achieve their achromatisms through varying combinations of glass types."
Achromatism is the reason early telescopes finally stopped painting every star with rainbow halos.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of achromatism
Achromatism comes from the Greek roots 'a-' meaning 'without' and 'chrōma' (genitive 'chrōmatos') meaning 'colour', combined with the suffix '-ism'. The related term 'achromatic' was coined in the late 18th century to describe lenses corrected for chromatic aberration, following John Dollond's mid-1700s work on achromatic refracting telescopes, and 'achromatism' developed alongside it as the noun denoting that property. It shares its Greek root with words such as 'chromatic', 'monochrome', and 'polychrome'.
Related word forms
How achromatism is actually used
A technical term used chiefly in optics and lens design; the broader 'colourlessness' sense is rare and largely confined to scientific or descriptive writing. Not used informally.
Easily confused with achromatism
Achromatism describes a property of optical lenses (or colourlessness in general), whereas achromatopsia is a visual condition in which a person cannot perceive colour.
Chromatic aberration is the colour-fringing defect itself, while achromatism is the correction or absence of that defect.