Patent ID: 6847482

Claim:
An image-erecting viewing optical system comprising a first prism having an incident surface and at least two reflection surfaces, a front lens group of an objective optical system, a second prism having an incident surface and at least two reflection surfaces, a rear lens group of said objective optical system, a field stop, and an eyepiece optical system, in this order from an object, wherein one reflection surface of one of said first prism and second prism comprises a roof-mirror surface; and wherein said first prism satisfies the following conditions: sin(0−ω′)>1 /n 6°<ω<16° wherein θ designates an angle between said incident surface and a first reflection surface of said first prism; ω designates a real field-of-view ω (half amount); ω′ designates an angle between a light ray of a real field-of-view ω (half amount) and the optical axis in said first prism; and n designates the refractive index of said first prism.