| 摘要 |
PROBLEM TO BE SOLVED: To provide a means for correcting scattering of focus position caused by an error of groove distribution pattern on a grid surface in a spectroscope using a diffraction grating with uneven interval groove. SOLUTION: A grating 13 held by a grating holder 15 is movable in the wave length direction (w axis). When a grating 13 is rotated around a rotation axis A-A of the grating holder 15 along the w-axis, the incidence point of the light on the grating plane 13a moves. As the results, a groove distribution function on the grating plane 13a for the incidence light practically varies and the scattering degree of the focus points of dispersed light coming out of the grating 13 also varies. By properly controlling the position of the grating 13, the scattering of the focus points can be made small.
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