In spectroscopic observations, sometimes you meet grism, sometimes grating.
Both of them could cause light dispersion, but what is the difference?
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$\begingroup$ Grism: en.wikipedia.org/wiki/Grism $\endgroup$ – Wayfaring Stranger Apr 21 '15 at 10:45
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$\begingroup$ I know that link. What is the function of a prism? A prism itself is enough to disperse light. $\endgroup$ – questionhang Apr 21 '15 at 11:04
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1$\begingroup$ They disperse light with different dispersion functions, allowing astronomers to see different spectral features. $\endgroup$ – Donald.McLean♦ Apr 21 '15 at 11:29
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Transmission gratings on their own introduce chromatic aberration. This is because they change the effective focal length and do so as a function of wavelength. The chromatic aberration can be eliminated by introducing a prism of the correct dispersion. Known as a grism, the grating/prism combination provides an unaberrated image at the 0th order in addition to the spectrum, although the spectrum has fairly low resolution.
