AbbeWert

AbbeWert, in optics, is the Abbe number of a material and serves as a measure of its chromatic dispersion in the visible spectrum. The term is named after Ernst Abbe, who introduced this concept to quantify how much a material’s refractive index changes with wavelength, an important factor in lens design.

The standard definition uses refractive indices at three Fraunhofer lines: V_d = (n_d − 1) / (n_F − n_C). Here n_d is the refractive index at the D-line (587.6 nm), n_F at the F-line (486.1 nm), and n_C at the C-line (656.3 nm). The Abbe number is dimensionless and typically reported for a given spectral range and temperature.

Interpretation and typical values: A higher Abbe value indicates lower dispersion and better resistance to chromatic aberration. Materials with low Abbe numbers disperse more strongly and are more challenging for achromatic designs. In practice, crown glasses often have moderate Abbe values (roughly 50–70), Flint glasses have lower values (often 30–50), and fluorite (CaF2) is among the highest for standard optical materials, around 90–100. Values depend on composition and measurement conditions.

Applications: The Abbe number is a key parameter in designing optical systems that minimize chromatic aberration. Achromatic doublets and apochromatic triplets are engineered by combining glasses with different Abbe numbers in addition to matching refractive powers. The Abbe value is one of several dispersion metrics and may vary with wavelength range and temperature, so designers specify the exact conditions under which V_d is reported.