GB147480A - Improvements in sighting devices - Google Patents

Abstract

147,480. Zeiss, C., [Firm of]. April 28, 1917, [Convention date]. Magnetic c o m - passes. - A sighting- device comprises a compass with a fixed graduated circle and a sighting - telescope rotatably mounted on the casing in such a manner that its axis of rotation coincides with the axis of the compass, and the axis of inspection coincides with the axis of rotation. The sighting-telescope consists of a reflecting prism a<1>, an objective a<2>, a roof prism a', and an eyepiece comprising lenses a<4>, a<5> between which is situated the prism a<6>. Lines A on the graticule disk a<8> are used as sighting lines. Rotation is effected by a worm c engaging a worm wheel b<1> on the compass casing b. To the upper portion of the compass case b is secured a graduated glass disk b<10>, over which rotates a disk b<7> having a zero mark b<8> (C, Fig. 3). The graduations and zero mark are projected into the outer portion of the field of view of the eyepiece by means of a lens e and a prism d in contact with the prism a<6> at the outer part of its hypotenusal face only. The object viewed is thus only visible in the middle portion of the field of view and the compass graduations and the compass direction indicator in the periphery of the field. The graduations D and indicator C may be illuminated by a lamp h in a recess at the side of the casing, from which also the graduated disk a<8> is illuminated through the prism i as shown. In use, the telescope is adjusted so that the point B coincides with the zero of the graduation D and the instrument is fixed in its support on the pivot b<2> so that the sighting line intersects the given directing point. This gives the direction of the line of sight with the magnetic meridian and then the telescope may be rotated to observe the desired object and the angle through which rotation is made read off directly.