The invention relates to an optical imaging system (20) comprising an illumination unit (23), a detection unit (24) and a measurement chamber (21) for receiving a subject to be examined, wherein the illumination unit (23) is arranged such in relation to the measurement chamber (21) that it can illuminate a subject placed inside the measurement chamber (21), and wherein the measurement chamber (21) is provided with several fins (31, 31′) for preventing stray light from reaching the detection unit (24), the several fins (31, 31′) being arranged in such a way that at least some of the fins (31, 31′) are in the field of view of the detection unit (24) with the fins (31, 31′) being orientated such that the surfaces (31.1, 31.1′) of the fins that are subjected to illumination by stray light are not visible to the detection unit (24).