Patent ID: 7061684
Filing Date: 2006-06-13
Classification: G02B

Abstract:
1. An observation optical system comprising: an image erecting optical system for forming an erect image of an object image; and an eyepiece optical system for observing the object image which has been formed into the erect image, wherein the image erecting optical system comprises at least one prism, an object-image-side, entrance surface of which comprises a convex surface, wherein the eyepiece optical system comprises, in order from an object-image side, a positive single lens having double convex surfaces and a negative meniscus lens having a concave surface directed toward an eye-point side, making it possible to observe the object image at a position, as an eye point, separated from an utmost eye-point-side surface of the eyepiece optical system by a distance of 17.4 mm, and satisfying the following conditions: where S=(r1−r2)/(r1+r2), r1 is a curvature radius of an object-image-side surface of the negative meniscus lens, r2 is a curvature radius of an eye-point-side surface of the negative meniscus lens, d 1 is an air space between the positive single lens and the negative meniscus lens where a value of the air space, if variable, is taken as d1 when a diopter of the observation optical system is adjusted to be −0.8 (m −1 ), f is a focal length of the eyepiece optical system, and IP is the distance from the utmost eye-point-side surface of the eyepiece optical system to the eye point, a value of which is 17.4 mm.