A relay optical system (1) for a rigid endoscope (12, 13) comprises twoidentically formed lens systems (2) which are arranged symmetrically to eachother with respect to a plane of symmetry (A) that is perpendicular to theopticalaxis (0). The lens systems (2) each comprise a first biconvex lens (4), abiconcavelens (5), a rod lens (6) having a convex lens surface (F5) facing the plane ofsymmetry (A) and a concave lens surface (F6) facing away from the plane ofsymmetry (A), and a second biconvex lens (7), in this order as viewed from theplane of symmetry (A).
