A device for dispersing light into a spectrum so that the intensity at each wavelength can be recorded by a detector. Spectrographs have been designed for use in various regions of the spectrum, with particular emphasis on the ultraviolet, visible, and infrared. Different wavelengths have different technological requirements—for example, many materials that are transparent at optical wavelengths are opaque in the ultraviolet. The main components of a traditional spectrograph include a slit, for selecting a particular object in the telescope field and to limit the instrumental width of spectral features; a collimator for focusing the light into a parallel beam; a disperser (a diffraction grating or prism), which splits the light into a spectrum; and a detector, nowadays usually a CCD, for recording the spectrum. The recorded spectrum is termed a spectrogram. The resolving power of the spectrograph is ultimately limited by the size of the disperser.