| 摘要 |
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<|tan 1°/(phi1-4-phi1-3)|<5 (mm) . . . (1) 0.5<SF4<1.0 . . . (2) wherein phi1-4 designates the combined power from the positive first meniscus lens element to the positive fourth lens element; phi1-3 designates the combined power from the positive first meniscus lens element to the negative third lens unit; and SF4 designates the shape factor of the positive fourth lens element defined as SF4=(r2+r1)/(r2-r1); r1 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.
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