将复色光分离成光谱的光学仪器。光谱仪有多种类型，除在可见光波段使用的光谱仪外，还有红外光谱仪和紫外光谱仪。按色散元件的不同可分为棱镜光谱仪、光栅光谱仪和干涉光谱仪等。按探测方法分，有直接用眼观察的分光镜，用感光片记录的摄谱仪，以及用光电或热电元件探测光谱的分光光度计等。单色仪是通过狭缝只输出单色谱线的光谱仪器，常与其他分析仪器配合使用。
The polychromatic light is separated into optical spectrum instrument. There are many types of spectrometers, in addition to the spectrometer in the visible band, as well as infrared spectroscopy and ultraviolet spectroscopy. According to the difference of dispersive elements, it can be divided into prism spectrometer, grating spectrometer and interference spectrometer. According to the detection method, a direct observation of eye plate records with a spectroscope, spectrograph, and photoelectric detection or thermoelectric element spectrum spectrophotometer. The monochromator spectrometer is only through slit output monochromatic spectral line, often used in conjunction with other analytical instruments.
图中所示是三棱镜摄谱仪的基本结构。狭缝S与棱镜的主截面垂直，放置在透镜L的物方焦面内，感光片放置在透镜L的像方焦面内。用光源照明狭缝S， S的像成在感光片上成为光谱线，由于棱镜的色散作用，不同波长的谱线彼此分开，就得入射光的光谱。棱镜摄谱仪能观察的光谱范围决定于棱镜等光学元件对光谱的吸收。普通光学玻璃只适用于可见光波段，用石英可扩展到紫外区，在红外区一般使用氯化钠、溴化钾和氟化钙等晶体。目前普遍使用的反射式光栅光谱仪有较宽的光谱范围。
Shown in Figure three is the basic structure of prism spectrograph. The slit S is perpendicular to the main section of the prism and is placed in the focal plane of the lens L, and the photosensitive film is placed in the image plane of the lens L. Using the light source to slit the S, the image of the S becomes a spectral line on the photosensitive film. Because of the dispersion of the prism, the spectral lines of different wavelengths are separated from each other. The spectral range of prism spectrograph can observe depends on prism optical elements on the absorption spectrum. Ordinary optical glass is only applicable to the visible light band, quartz can be extended to the UV region in infrared region using sodium chloride, potassium bromide and calcium fluoride crystal. The widely used reflection grating spectrometer has a wide spectral range.