| 摘要 |
PROBLEM TO BE SOLVED: To provide a film reading device having excellent use efficiency of light and to provide a diffusion optical element and an illumination optical system suitable for that device. SOLUTION: The diffusion optical element produced by using holography and set in such a manner that the reduction rate in the intensity from the direction of the highest intensity is small for light in the wavelength region with high incident intensity and that the reduction rate is large for light in the wavelength region with low incident intensity. Therefore, the light in the wavelength region with the lower incident intensity is diffused in the narrower angle range, and by using the diffused light in a specified angle range from the direction of the highest intensity, the use efficiency in the wavelength region with low intensity can be increased. The illumination optical system is equipped with the aforementioned diffusion optical element, and the illumination optical system is used to illuminate a film.
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