An optical rotary joint comprises means for coupling-in or coupling-out light, and an optical derotating system. The derotating system may be a Dove prism or an Abbe-Koenig prism. In order to improve reflection at a reflecting face or faces of the derotating element, the reflecting faces are coated with an optically transparent material having a refractive index that is lower than the refractive index of the derotating element. In an embodiment the derotating optical element comprises a Dove prism. Light entry and light exit faces of the Dove prism are provided with optical supplementary elements that have an optical index of refraction greater than an optical index of refraction of the Dove prism.