| Astrophysics (Index) | About |
A grism (or grating prism) is a prism in which one surface is shaped as a grating (stair-steps), which disperses electromagnetic radiation passing through by wavelength both through the prism effect and the grating's diffraction. Grisms are used as dispersers for some spectrographs (i.e., grism spectrographs), the term grism spectroscopy commonly used for their use. The general direction of the dispersed EMR can be straight through, and an instrument can be constructed that can also act as a simple imager by shifting the grism out of the optical path. It also allows the instrument to be compact, which is very useful for space telescopes. Example instruments incorporating a grism: