Viewing optical system with an image-blur correcting optical system

Abstract

A viewing optical system includes an objective optical system and an eyepiece optical system. The objective optical system includes a positive first meniscus lens element having the convex surface facing toward the object, a positive second meniscus lens element having the convex surface facing toward the object, a negative third lens unit constituted by two negative lens elements, and a positive fourth lens element. The fourth lens constitutes an image-blur correcting optical system movable in a direction perpendicular to the optical axis. The viewing optical system satisfies the following conditions: 0.5<&verbar;tan 1&deg;/(&phgr; &minus;&phgr; )&verbar;<5 (mm) . . . (1) 0.5<SF <1.0 . . . (2) wherein &phgr; designates the combined power from the positive first meniscus lens element to the positive fourth lens element; &phgr; designates the combined power from the positive first meniscus lens element to the negative third lens unit; and SF designates the shape factor of the positive fourth lens element defined as SF &equals;(r &plus;r )/(r &minus;r ); r designates the radius of curvature of the object-side surface of the positive fourth lens element; and r2 designates the radius of curvature of the image-side surface of the positive fourth lens element.