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diffraction grating comparison table

Subject	has definition
blazed grating	Diffraction grating so ruled that the reflected light is concentrated into only a few orders, or even a single order, of the spectrum.
echelle	A type of diffraction grating with groove angles of 90°. With the grating at an angle of 45° the grooves resemble a staircase.
grism	This is a right-angled glass prism with a transmission diffraction grating deposited on the hypotenuse surface. The spectrum produced by the grating is deflected by the prism to remain on the optical axis and the apex angle of the prism is chosen to get a certain wavelength in the center of the detector. Grisms can be placed in a filter wheel.
objective grating	A coarse grating placed in front of the telescope objective.

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