内視鏡用対物レンズ

Japanese Patent JP5226882

B2

PROBLEM TO BE SOLVED: To provide an objective lens for endoscope, which can be reduced in variation of a field angle, sufficiently corrected in aberration, and reduced in size.SOLUTION: The objective lens for endoscope has lens groups G1 and G2 with a diaphragm S between them. The group G1 is composed of a negative meniscus first lens with a convex face on the object side and a positive second lens. The group G2 is composed of a positive third lens whose aspheric face is oriented toward the image side and whose curvature becomes gentle from its center toward its periphery, and a cemented lens formed from a positive fourth lens and a negative fifth lens. The objective lens satisfies the following expression: -2