| 摘要 |
An observation optical system of the present invention comprises an image erect optical system and an eyepiece optical system for observing an object image. The eyepiece optical system comprises a positive single lens having double convex surfaces and a negative meniscus lens having a concave surface directed toward eye point side, and the following condition is satisfied: 0<S<0.3 0.05<d1/f<0.15 where S=(r1-r2)/(r1+r2), r1 is a curvature radius of the object image side surface of the negative meniscus lens, r2 is a curvature radius of the eye point side surface of the negative meniscus lens, d1 is a distance of air space between the positive single lens and the negative meniscus lens, which represents a distance of air space when diopter of the observation optical system is adjusted to be -0.8 (m<-1>) if the air space is changed, and f is a focal length of the eyepiece optical system.
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