spectrograph

A spectrograph is an instrument to record the spectrum of incoming light, a practice termed spectrography. In the case of modern advanced instruments, the terms spectroscope, spectrograph, and spectrometer are used interchangeably. Spectrographs are used as lab instruments and telescope instruments.

The term spectrograph was coined for a device that guides light through a disperser (prism or grating) to lay out the spectrum spatially and focuses this on photographic film, recording it for later study. This is in contrast to a spectroscope, which was used for a device that you look through to observe the spectrum, so a spectrograph was much like a spectroscope with a camera attached. The term spectrometer was coined for devices that measure aspects of the spectrum, a general term that pretty much applies to either.

Modern advanced instruments virtually always focus the spectrum on a CCD or analogous sensor, allowing the spectral data to be transmitted, recorded and analyzed electronically, and all three terms are commonly used for such instruments. The terms may be used for analyzers of any part of the electromagnetic spectrum, but when used for other than visible light, that is often mentioned, e.g., the phrase "X-ray spectrometer".