A method and an apparatus are used for detecting optical systems, for example a sniper within a terrain. The terrain is optically scanned by means of a movable mirror and the position of the optical system is determined from a measurement made by a laser unit and is optically displayed. The position of the optical system is directly determined from the measurement made by the laser unit by evaluating the intensity of a light beam from the laser unit, after having been reflected by an optical surface of the optical system. The position is optically reflected into the field of vision of a telescope. The apparatus comprises a laser unit having a movable mirror, a control unit for detecting the position of the optical system from a measurement made by the laser unit, and a device for optically displaying the position. The device for optically displaying is a telescope, and means are provided for optically reflecting the position of the optical system into the field of vision of the telescope.