The invention concerns optical devices enabling an electronic image to be superimposed to an image from an exterior landscape. The invention concerns an optical device for superimposing images designed to be arranged in front of an optical module comprising at least one lens and a photosensitive surface arranged in the focal plan of said lens. The device comprises at least one source of images (20), one relay optics (21) and an optical mixer (23) consisting of two optical components (230, 231) assembled by a substantially planar common surface (28) including a hardly reflecting processing. The mixer is globally shaped like a blade with planar and parallel surfaces, the common surface being inclined by about 45 degrees relative to said planar surfaces. It comprises an input surface (27) and an opposite surface (26) substantially perpendicular to the planar surfaces (24, 25); the opposite surface (26) having substantially the shape of a reflecting spherical diopter. Said device is particularly useful for night vision binoculars wherein, when the optical mixer is placed in front of the lens (10) of a binocular body, it enables an electronic image external to the landscape to be superimposed by introducing a marginal attenuation.