stigmatic concave grating

stigmatic concave grating

[stig′mad·ik ′kän‚kāv ′grād·iŋ]
(optics)
An optical element with many parallel grooves on a concave optical surface; combines the two functions of light dispersion and focusing in one dispersive element; used in space optics, in food and metal analysis, and as a dispersive element of spectrophotometers and spectrographs.