Optical system, in particular an OCT scanner, comprising an optical coherence tomography, OCT-, measuring device and a beam deflection unit for laterally deflecting the position and/or angle of a beam path of the OCT measuring device, wherein ▪ there is an optical component in the beam path, said optical component being embodied in such a way that a back-reflection of the optical component has a different configuration in terms of its longitudinal location along the beam path depending on the lateral position of the deflected beam path, and ▪ the optical system comprises an evaluation unit which is embodied in such a way that a value of the lateral position and/or angle deflection of the beam deflection unit is determined on the basis of a longitudinal location of the back-reflection at the optical component determined during the OCT measuring, and the determination of the position and/or angle deflection of the deflection unit as well as an optical measuring of a test object is done with the same OCT-radiation and the optical component is arranged in the beam path downstream of the beam deflection unit and the optical component is arranged and embodied in such a way that the optical component is transmitted by the beam path. an optical coherence tomography, OCT-, measuring device and a beam deflection unit for laterally deflecting the position and/or angle of a beam path of the OCT measuring device, wherein ▪ there is an optical component in the beam path, said optical component being embodied in such a way that a back-reflection of the optical component has a different configuration in terms of its longitudinal location along the beam path depending on the lateral position of the deflected beam path, and ▪ the optical system comprises an evaluation unit which is embodied in such a way that a value of the lateral position and/or angle deflection of the beam deflection unit is determined on the basis of a longitudinal location of the back-reflection at the optical component determined during the OCT measuring, and the determination of the position and/or angle deflection of the deflection unit as well as an optical measuring of a test object is done with the same OCT-radiation and the optical component is arranged in the beam path downstream of the beam deflection unit and the optical component is arranged and embodied in such a way that the optical component is transmitted by the beam path. ▪ there is an optical component in the beam path, said optical component being embodied in such a way that a back-reflection of the optical component has a different configuration in terms of its longitudinal location along the beam path depending on the lateral position of the deflected beam path, and ▪ the optical system comprises an evaluation unit which is embodied in such a way that a value of the lateral position and/or angle deflection of the beam deflection unit is determined on the basis of a longitudinal location of the back-reflection at the optical component determined during the OCT measuring, and the determination of the position and/or angle deflection of the deflection unit as well as an optical measuring of a test object is done with the same OCT-radiation and the optical component is arranged in the beam path downstream of the beam deflection unit and the optical component is arranged and embodied in such a way that the optical component is transmitted by the beam path.