Abstract: Binoculars which can adjust the optical axes of optical systems by moving at least one lens groups of objective lens groups and eye piece groups in a plane approximately perpendicular to the optical axes of the lens groups and further independently adjust the optical axes of the optical systems in a linear direction and in the direction approximately perpendicular to the linear direction by moving, one lens groups of the objective lens groups and the eye piece groups on the plane approximately perpendicular to the optical axes of the lens groups approximately in the linear direction and moving the other lens groups of the objective lens groups and the eye piece groups on the plane approximately perpendicular to the optical axes of the lens groups approximately in the linear direction, whereby the optical axis between a pair of the right and left optical systems of the binoculars can be easily adjusted.

Abstract: A prism optical system provided with: a first prism on which a light ray coming from an objective lens is incident; a second prism on which the light ray coming from this first prism is incident, and from which this incident light ray is emitted; and a plate-like member which is interposed between the aforesaid prisms so as to provide a predetermined air space therebetween and which has a diaphragm opening and a light blocking portion. Further, an uneven portion, which consists of depressions and projections and has a serrate section, for preventing light rays, which have been reflected from the surface of the light blocking portion of this plate-like member, from entering a field stop is provided in the light blocking portion thereof. Thereby, occurrences of ghosts and flares due to stray light are prevented. Moreover, ghosts and flares are reduced.