| 摘要 |
In order from the object side, a first lens having positive power with a convex observation-side surface, a second lens having negative power and a meniscus shape with a concave object-side surface, and a third lens having positive power with an observation-side surface having a smaller radius of curvature than that of an object-side surface are provided. The first, second and third lenses are single lenses. The conditional expressions (1): 0.9<f1/f3<5.0, (2): 10.0<TL<17.0 and (3): 15.0<f<25.0 are satisfied at the same time, where f1 is a focal length of the first lens, f3 is a focal length of the third lens, f is a focal length of the entire system, and TL is a distance along an optical axis from an object-side lens surface of the first lens to the observation-side lens surface of the third lens. |
| 主权项 |
1. An eyepiece optical system substantially consisting of, in order from an object side:
a first lens having a positive refractive power with an observation-side lens surface being a convex surface; a second lens having a negative refractive power and having a meniscus shape with a concave surface facing the object side; and a third lens having a positive refractive power with an observation-side lens surface having a smaller radius of curvature than a radius of curvature of an object-side lens surface, wherein each of the first lens, the second lens and the third lens consists of a single lens, and the conditional expressions (1), (2) and (3) below are satisfied at the same time:
0.9<f1/f3<5.0 (1),10.0<TL<17.0 (2) and15.0<f<25.0 (3),where f1 is a focal length of the first lens, f3 is a focal length of the third lens, f is a focal length of the entire lens system, and TL is a distance along an optical axis from an object-side lens surface of the first lens to the observation-side lens surface of the third lens. |
