| 摘要 |
[Problem] To provide an invention comprising, in order from the object side, a first lens (L1) with an observation-side lens surface (S1k) forming a convex surface and having a positive refracting power; a second lens (L2) with a concave surface facing the object side, having a meniscus shape, and having a negative refracting power; and a third lens (L3) with an observation-side lens surface (S3k) having a curvature radius smaller than the curvature radius of an object-side lens surface (S3b) and having a positive refracting power; wherein each of the first (L1), second (L2), and third (L3) lenses is configured as a single lens, and is configured to simultaneously satisfy the following condition expressions: (1) 0.9 < f1/f3 < 5.0, (2) 10.0 < TL < 17.0, and (3) 15.0 < f < 25.0; where f1 indicates the focal-point distance of the first lens (L1), f3 indicates the focal-point distance of the third lens (L3), f indicates the focal-point distance for the complete lens system, and TL indicates the distance on the optical axis from the object-side lens surface of the first lens (L1) to the observation-side lens surface of the third lens (L3). |
