A detector (118) for determining a position of at least one object (112) is disclosed, the detector (118) comprising: at least one longitudinal optical sensor (120), wherein the longitudinal optical sensor (120) has at least one sensor region (124), wherein the longitudinal optical sensor (120) is at least partially transparent, wherein the longitudinal optical sensor (120) is designed to generate at least one longitudinal sensor signal in a manner dependent on an illumination of the sensor region (124) by at least one light beam (126) traveling from the object (112) to the detector (118), wherein the longitudinal sensor signal, given the same total power of the illumination, is dependent on a beam cross-section of the light beam (126) in the sensor region (124); at least one illumination source (114) adapted to illuminate the object (112) with illumination light (115) through the longitudinal optical sensor (120); and at least one evaluation device (136), wherein the evaluation device (136) is designed to generate at least one item of information on a longitudinal position of the object (112) by evaluating the longitudinal sensor signal.