A detector (110) for optically detecting at least one object (112) is proposed. The detector (110) comprises at least one optical sensor (114). The optical sensor (114) has at least one sensor region (116). The optical sensor (114) is designed to generate at least one sensor signal in a manner dependent on an illumination of the sensor region (116). The sensor signal, given the same total power of the illumination, is dependent on a geometry of the illumination, in particular on a beam cross section of the illumination on the sensor area (118). The detector (110) furthermore has at least one evaluation device (122). The evaluation device (122) is designed to generate at least one item of geometrical information from the sensor signal, in particular at least one item of geometrical information about the illumination and/or the object (112).