Problem to be solved: to provide an illumination optical system in which a good observation can be performed in the proximity observation and in addition to observation of far points, and the unevenness in light distribution of illumination light is reduced.Solution: the first lens comprises a first lens having a positive refractive power, a second lens having a positive refractive power and a third lens having a positive refractive power, and the first lens is a convex surface on the object side, and the surface of the light source side is an aspherical surface, and the following conditional expressions (1) and (2) are satisfied.3 . Rho. \/ R2. Vertline. 7 (1)2 . Phi. \/. Zasp ZSPH. Vertline. 16 (2)Here, R1 is the radius of curvature of the object side of the first lens, R2 is the radius of curvature of the light source side of the first lens, & phgr is the half of the diameter of the light beam incident on the third lens, zasp is the zag amount at the light height. Phi. In the aspherical surface of the first lens of the first lens, ZSPH is the first lens The zag amount at the beam height φ of the paraxial reference sphere in the aspherical surface of the light source side.Diagram【課題】遠点観察に加え、近接観察においても、良好な観察をすることができ、照明光の配光ムラが低減された照明光学系を提供する。【解決手段】物体側から順に、正屈折力を有する第1レンズと、正屈折力の第2レンズと、正屈折力を有する第3レンズと、からなり、第1レンズは、物体側に凸面を向け、かつ、光源側の面は非球面であり、以下の条件式(1)、(2)を満足する。 3<|r1/r2|<7 (1) 2<φ/|Zasp-Zsph|<16 (2) ここで、r1は、第1レンズの物体側面の曲率半径、r2は、第1レンズの光源側面の曲率半径、φは、第3レンズに入射する光束の径の半分の長さ、Zaspは、第1レンズの光源側の非球面における、光線高さφにおけるザグ量、Zsphは、第1レンズの光源側の非球面における、近軸参照球面の光線高さφにおけるザグ量、である。【選択図】図1
