Patent GB-124497-A (GB)
Title: Improvements in or relating to Optical Observing Means, with special reference to Range Finding.
IPC: G01C3/10
Filed: 1916-02-07
Abstract: 124,497. Grubb, Sir H., and Vickers, Ltd. Feb. 7, 1916. Optical squares.-Apparatus for determining the range of aircraft and other objects comprises two sighting instruments which differ in character and are separated by a long home-base, the instruments being so constructed that the observer at one of them can determine the range without communicating with the other observer; the apparatus may also be used to determine the angular relation between the axis of an instrument, and an axis, which may be that of another instrument, at a distance. As shown diagrammatically in Fig. 1, one instrument B consists of a telescope carrying a mirror m, and the other instrument A consists of a telescope having two object glasses o p, with perpendicular axes, and a Prandl prism c so placed that the two fields of view are visible in one eye-piece. The instrument A carries a lamp or the like above the optical centre of the object glass o, and the image of the lamp produced by the mirror m and the object glass p constitutes an index image which is central in the field of view of the telescope A when the axes of the telescope and mirror are parallel. A scale may be provided, visible in the field of view, so that the index image may indicate the angular relation between the axis of the telescope A and the mirror. When using the apparatus for determining the range of an object, the observer at the instrument B adjusts the instrument during the observation so as to maintain the image of the object upon the cross wires, and the observer at the instrument A manipulates means w until the image of the object produced by the object glass o and the index image are brought into coincidence, the range being then indicated by a fixed pointer on a scale carried by the means w and visible in the lower part of the field of view. The instrument B is mounted so as to be completely rotatable about an axis in the direction of the base, and so as to be adjustable through about 2‹ in the plane of observation by means of a controlling screw. The mirror m is secured to the telescope at three points with its plane parallel to the axis thereof, and is furnished with a deep rib to prevent distortion. The instrument A is capable of universal motion and is constructed as shown in Fig. 10. The object glass o is placed so as to form an image in the upper half of the tube 10, and the object glass p is mounted at the outer end of one of the horizontal trunnions, the trunnions being tubular. The Prandl prism 13 is preferably placed so as to bend a ray along the axis of the object glass p into the axis of the tube 10. The means for making coincidence may comprise a pair of rotatable prisms 14, 15, such as are described in Specification 25682/03, which are turned by a button 18 through bevel gearing, the prism 14 having a scale of ranges engraved upon it. The scale is illu. minated by a lens or aperture 19, and a lens 20 produces an image of it in the lower part of the tube 10. The eye piece is perpendicular to and rotatable about the axis of the tube 10, the images being observed with the aid of a right-angled prism 23, a lens 22, and prisms 21. The instruments may be mounted on a base beam capable of being turned so as to be approximately at right angles to the line of sight to the object. The beam may be trussed or comprise a steel tube closed at the ends and stiffened by means of compressed air within it. The beam may be mounted on a pivot at one end or at its centre, the other end or both ends travelling on a circular rail track or being carried by caissons floating on water in a circular channel. The ends of the beam may alternatively travel on straight intersecting slides, its centre being carried if desired by a trolley travelling on a circular track. The beam may be dispensed with, one of the instruments being located at the centre of a circular track and the other being carried by a truck travelling on the track.