Raman scattered light may be weak, so some sensitivity, brightness (detected intensity to background), etc. are required. There is a numerical value representing the brightness of the spectrometer called “f value”. The f value decreases as the focal length is shorter and the value becomes brighter, but the optical efficiency does not mean what it should be as an absolute value, but the f value on the side of the spectroscope and the incident light source is matched It is important. For example, if the light source side is too bright compared to the f-number of the spectrometer, the light will spread to the outside of the diffraction grating and become stray light. You Some of the commercially available devices have different f-numbers, but because they have their own appropriate optical system, it can not be said in general that “the f-number of the spectrometer is small = bright, good sensitivity”. So be careful when comparing the specifications.