Abstract: An optical control unit comprises a base and at least one optical assembly having optical emitting means and conjugate optical receiving means with preset and fixed focal distances, the optical emitting means and conjugate optical receiving means being associated with the base so as to have fixed orientations with respect to the base and be capable of movement in directions parallel and transverse to the face of the base. The optical control unit is positioned with respect to the object to be inspected, and the optical emitting means and conjugate optical receiving means are sighted on a selected region of the wall of the object, the adjustment of sighting being accomplished through simple translations of the optical emitting means and receiving means while maintaining their orientations on the optical control unit unchanged.