| 摘要 |
PROBLEM TO BE SOLVED: To provide an illumination optical system having stable performance, a small size and a wide light distribution range, in which nonuniform illumination, such as nonuniform light distribution or nonuniform color is reduced more than in conventional illumination optical systems, and to provide an illumination device using the illumination optical system, and to provide an observation system using the illumination optical system or the illumination device that uses the illumination optical system. SOLUTION: In the illumination optical system 2 disposed in order to diffuse illuminating light emitted from a light source, at least one face r<SB>2</SB>of an optical element composing the illuminating optical system 2 is a grained face, and the arithmetic average roughness of the grained face is set to a range of 0.05 to 0.75 [μm]. In addition, the number of planar undulations of the grained face r<SB>2</SB>is 20 or smaller in the direction of the diameter of the optical element. The PV value of the planar undulations of the grained face r<SB>2</SB>of the optical element is 50 [μm] or smaller. COPYRIGHT: (C)2006,JPO&NCIPI
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