GB844964A - Levelling instrument with automatic compensation for small inclinations of the instrument - Google Patents

Abstract

844,964. Stabilizing line of sight; levels. HENSOLDT & SOHNE, OPTISCHE WERKE A. G., M. Nov. 4, 1957 [Nov. 2, 1956; March 14, 1957], No. 34280/57. Classes 97(1) and 97(2) Automatic compensation for small inclinations of a levelling instrument is provided by at least one afocal pair of lenses, of which one lens is fixed to the instrument, and the other is pendulously suspended about an axis perpendicular to the optical axis of the instrument, and spaced from the principal point of the lens by a distance equal to the focal length. There may be n such pairs of lenses, the pendulous lenses of each pair being pivoted about a common axis, so that where ri is the distance of the principal point of the ith pendulously suspended lens from said axis, #i being the refractive power of this lens, and n being the number of lens pairs. When a further optical system, for example a mirror or prism is fixedly arranged in front of the i<th> lens pair, the condition to be satisfied is where Ni is the magnification of the further optical system. As shown in Fig. 1 a, the telescope 1 of a levelling instrument, having a graticule 2 between the objective and eyepiece has attached thereto a device 4, carrying a fixed negative lens 5 and a positive lens 6 of numerically equal focal lengths. Lens 6 is pendulously suspended by balance weights 8, 81 about an axis 7, orthogonal to the optical axis and spaced from lens 6 by its focal length, so that upon small inclinations of the instrument, the lenses 5, 6 act as an optical wedge, and ensure that a horizontal ray from a target remains focused on the graticule 2. In the arrangement of Fig. 2, the lens pair 21,22 are mounted between fixed prisms 20,24 and lens 21 is pendulously suspended under its own weight from an axis 23. Fig. 3 shows two lens pairs 30,31 and 32,35, the lenses 31,33 being pendulously suspended from a shaft 34, disposed at a distance from each of the pendulously suspended lenses equal to half the focal length thereof. A roof edge prism may be disposed between the lens pairs, or between the second lens pair and the telescope objective. In Fig. 11, a telescope 102 is shown, which is rotable about a vertical axis on a base which can be levelled by adjustable feet 100 and a bubble level 110. Light enters the telescope through rotatable wedges 108, and is directed upwards by prism 107, and compensation for small deviations from the vertical is effected by afocal lens pairs 112,113 and 114,115, the lenses 113,114 being pendulously suspended by three threads 120. Specification 721,434 is referred to.