| 摘要 |
PROBLEM TO BE SOLVED: To insert and arrange an optical path converting prism between a solid-state image pickup element and the objective by composing a front-group diverging lens system of a 1st lens and a rear-group converging lens system of a 2nd lens and a cemented lens of a 3rd and a 4th lens. SOLUTION: The 1st lens L1 which has a surface with a small radius of curvature on its image plane side and also has negative refracting power, the 2nd lens L2 which has a surface with a small radius of curvature on its image plane side and also has positive refracting power, the 3rd lens L3 consisting of a convex lens, and the 4th lens L4 consisting of a concave lens are arranged in order from the object side, and the 3rd and 4th lenses L5 and L4 are constituted as the cemented lens. The 1st lens L1 constitutes the front-group diverging lens and the 2nd to 4th lenses L2 to L4 constitute the rear-group converging lens. Then the objective satisfies dx>=3.0×|f1|. Here, f1 is the focal length of the 1st lens L1 and dx is the interval between the rear-side principal point of the 1st lens L1 and the front-side principal point of the rear-group converging lens system.
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