| 摘要 |
PROBLEM TO BE SOLVED: To provide an imaging lens for a capsule endoscope with improved distortion. SOLUTION: The capsule endoscope has the imaging lens 45a to form the image of a substantially spherical subject 40 in a plane shape on an imaging surface. The imaging lens 45a is composed of four lenses consisting of first-fourth lenses L1-L4 and an aperture diaphragm S8, which are arranged in the order from the object side, starting from a first lens group G1 with negative refraction, the aperture diaphragm S8, and a second lens group G2 with positive refraction. The first lens L1 is a meniscus-shaped lens with the convex surface turning toward the object side, and the curvature of the image-side surface S5 is larger than the curvature of the object-side surface S4. The second lens L2 is a meniscus-shaped lens with the convex surface turning toward the image side, and the curvature of the image-side surface S7 is larger than the curvature of the object-side surface S6. The surface shapes and disposition of the first-fourth lenses L1-L4 are in consideration of a front cover 41 of the capsule endoscope and a glass cover 56 of an imaging device. COPYRIGHT: (C)2009,JPO&INPIT
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