Viewing optical instrument

摘要

A viewing optical instrument includes an objective optical system and an eyepiece optical system such that an object image formed through the objective optical system is magnified and observed through the eyepiece optical system. The viewing optical instrument includes an eyepiece adjusting device which allows the eyepiece optical system to rotate relative to the objective optical system about a rotational axis at which an optical axis of the objective optical system intersects a focal plane formed by the objective optical system. A detector detects an inclination of a surface of a sighting object relative to a plane which is normal to the optical axis of the objective optical system, and a controller control the eyepiece optical system to rotate about the rotational axis in accordance with the inclination detected by the detector.