Abstract: A method and apparatus for determining a range of sight which are capable of monitoring and correcting the operability of the instrument. A light emitter directs an emitted light beam to a measurement zone and a light receiver receives a received light beam from the measurement zone. The emitted light beam and the received light beam cross each other in the measurement zone. A deflector deflects at least a portion of the emitted light beam downstream of the measurement zone along a light transmitting path and directs the portion of the emitted light beam into the received light beam at a side of the measurement zone opposite from the light receiver. An optical shutter intermittently closes the light transmitting path in a temporally controlled manner.

Abstract: A method and apparatus for determining a range of sight which are capable of monitoring and correcting the operability of the instrument. A light emitter directs an emitted light beam to a measurement zone and a light receiver receives a received light beam from the measurement zone. The emitted light beam and the received light beam cross each other in the measurement zone. A deflector deflects at least a portion of the emitted light beam downstream of the measurement zone along a light transmitting path and directs the portion of the emitted light beam into the received light beam at a side of the measurement zone opposite from the light receiver. An optical shutter intermittently closes the light transmitting path in a temporally controlled manner.

Abstract: An optical autocollimation measuring apparatus has a light transmitter-receiver arranged in a housing (15). An image of the light source (11) is formed in the objective (12) by a condensor (9) through the beam divider (20). The objective (12) in turn forms an image of the exit pupil of the condensor (9) in the plane of the retroreflector via the measuring path (13). The retroreflector (14) reflects the incident light beam substantially back on itself to the housing (15) of the light transmitter-receiver, where the received light beam is deflected by the beam divider (20) to a photoreceiver (21). A deflecting mirror (16) is located between the front objective (12) and the measuring path (13) and consists of two parts which are pivotable relative to one another, about a pivot axis (25) extending perpendicular to the optical axis (17), from an extended position into a position in which they are displaced by 90.degree. relative to one another.

Abstract: A beam divider which is particularly intended for use in smoke measuring apparatus comprises a transparent beam dividing plate (11) which is obliquely arranged in the beam path and is partially silvered at its lower side (11'). Two protective plates (13, 14) which form a closed internal space (12) leave the upper side of the beam dividing plate (11) above and below the optically active region. At least the protective plate (13) which crosses the beam path is transparent and the arrangement is closed in a dust-tight manner at the end faces.