| 摘要 |
An objective lens particularly suitable for use in endoscope, employing a lens system which is composed of four single lenses, namely, composed of, from the object side, a first lens L1 consisting of a negative lens having the concave surface thereof on the object side, a second lens L2 consisting of a positive lens having a surface of smaller radius of curvature disposed on the object side, a third lens L3 consisting of a positive lens having a surface of smaller radius of curvature on the image side, and a fourth lens L4 consisting of a positive lens. In this lens construction, the respective lenses L1 to L4 are adapted to satisfy the conditions of n1>1.70, gamma 1>40.0, gamma 3<42.5, n5>1.60, gamma 5>50.0, n7>1.60, and gamma 7>50.0 (where n1, n5 and n7 are refractive indices of the first lens L1, third lens L3 and fourth lens L4 relative to line d, respectively, and gamma 1, gamma 3, gamma 5 and gamma 7 are Abbe's numbers of the first to fourth lenses L1 and L4, respectively.
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