| 摘要 |
PROBLEM TO BE SOLVED: To obtain high-contrast observation by providing a specified optical system, including an erect prism in the optical system and making one prism out of the erect prism satisfy a specified condition. SOLUTION: This optical system satisfies the condition 2<fo <fE, and one prism out of the erect prism arranged in the optical system has optical material satisfying the conditionνd <50. Provided that fo is the focal length of an objective lens, fE is the focal length of an ocular system andνd is the Abbe number of the prism. By making one prism out of the erect prism satisfy the conditionνd <50, the chromatic aberration of the magnification of the optical system is corrected without imposing a burden on the negative lens of the ocular system. Therefore, it is unnecessary to make the power of the negative lens strong such as making the curvature of the negative lens of the ocular lens system intense or the thickness thereof large in order to correct the chromatic aberration of the magnification of the optical system. Therefore, the ocular system is miniaturized even in the optical system having strong power which satisfies the condition 2<fo <fE.
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