An optical system for a stereo-video endoscope, the optical system including: first and second lens system channels having first and second optical elements on first and second optical axes, respectively, the first and second optical axes being parallel to each other; wherein the first and second optical elements are each arranged symmetrically relative to each other about a plane of symmetry between the first and second lens system channels and the first and second optical elements comprise first and second D-cut lenses, respectively, each of the first and second D-cut lenses having a boundary surface which is set back relative to the plane of symmetry; and the boundary surface of each of the first and second D-cut lenses are inclined with respect of the plane of symmetry.