GB1426447A - Device for determining the angle between two directions - Google Patents

Abstract

1426447 Optical apparatus BOFORS A B 5 April 1973 [5 April 1972 20 March 1973] 16419/73 Heading G2J Sighting apparatus for determining, or providing a control signal dependent upon, the angle subtended at the apparatus by the separation between a first movable object having a light source (e.g. missile 12 with tracer 11) and a point on a second object (e.g. target 13) comprises two optical paths one of which includes a deflector e.g. mirror 6 adjustable by the observer and one of which includes means e.g. a rotating wedge prism 9 for oscillating the image so that detail cannot be seen but the light source appears as a predetermined pattern e.g. a circle. The deflector 6 is adjusted to bring the image of the second object into the correct relation with this pattern and this adjustment produces the required angular determination or control signal, e.g. for guiding the missile. In the embodiment of Fig. 1 the two paths enter a single objective 1 to be divided and later recombined by beam-splitters 3, 5. In a modification Fig. 2 (not shown) two objectives are provided, one for each path. One path includes the adjustable mirror and oscillating prism and the two paths are combined in a beamsplitter. In another embodiment Fig. 3 (not shown) two objectives and two eye-pieces are employed, the two paths thus being kept separate for recombination in the observer's brain. In this embodiment the deflector is a pair of rotatable wedge prisms while oscillation is as above. In a further embodiment Fig. 4, (not shown) the oscillation is a horizontal sweep. Light is reflected through 90 degrees by a prism, passes through a rotating wedge prism, is reflected through 180 degrees by a roof prism, passes through the wedge prism again and is reflected through 90 degrees by a further prism to the eye of the observer. A rotating bar extinguishes the light at the centre point of the sweep. In a still further embodiment Figs. 5, 6, (not shown) the two paths enter a single objective and are divided by a rotating, part reflecting, part transmitting chopper disc at 45 degrees to the incident light. The reflected light is again reflected by a fixed prism while the transmitted light is oscillated by a rotating wedge prism and is reflected by the adjustable mirror. The two paths then recombine in a splitting prism before reaching an eye-piece. The oscillation may be effected by the chopper. A rotating, instead of rotating, oscillation may be produced by a turning prism.