A spectrograph is a spectroscope fitted with a camera or an electronic detector such as a charge-coupled device (CCD) used to obtain a permanent record of the spectrum so that the intensity at different wavelengths can be measured. It consists of a slit for isolating the light from a particular object in the telescopes field of view, a collimator for directing this light into a parallel beam, a diffraction grating or prism for creating the spectrum, and a detector for recording the spectrum. In the past the detector would have been a photographic plate but today CCDs, which are far more sensitive, are typically used instead.
An échelle spectrograph is a spectrograph that uses an échelle grating to achieve high spectral resolution and wide wavelength coverage. The overlapping spectra produced by the grating are separated by a prism or a grism before reaching the detector. The sensitivity brought to modern échelle spectrographs by CCD detectors has made them indispensable in such fields as astroseismology and exoplanet searches.