Patent ID: 8730471

Claim:
A spectroscopic optical system comprising: an illumination optical system including a light source, a folding mirror, a field stop, and an object-side objective lens system for illuminating a sample; a detection optical system including the object-side objective lens system, the field stop, the folding mirror, and an image-side focusing lens system disposed on an image forming plane on the object side; and a spectroscope for separating specularly reflected light from the sample, wherein: the object-side objective lens system and the image-side focusing lens system are color corrected in a broad range of wavelengths from 190 to 400 nm, the two systems being formed only by refractive lenses, and the working distance (WD) of each lens is set so as to satisfy the following equation (1): WD≦10.0 mm, (1) a distance D between each of the adjacent lenses within each doublet is set so as to satisfy the following equation (2): (λ1·λ2)/4 nγ≦D (2) n is a refractive index of air and γ is a spectroscopic resolution, λ 2 is a wavelength to be studied, which is determined by selecting the longest wavelength of all the wavelengths in the range to be studied, and λ 1 is obtained by adding the spectroscopic resolution y to the target wavelength λ 2 .