Abstract: A two-stage multi-spectral imaging system comprising a reflective objective and a reflective relay aligned on a common optical axis, the objective being arranged to form an intermediate image and the relay being arranged to deliver image-forming radiation emanating from the intermediate image to a focal plane, wherein the objective is formed by a large concave primary mirror which is apertured on-axis and a small secondary mirror generally disposed in the form of a “Cassegrain” objective, the relay is formed by a pair of confronting mirrors each being apertured on-axis to enable passage of radiation into and out of the relay, and the relay being positioned to provide space between the relay and the focal plane to accommodate waveband selective splitting optics if so desired.

Abstract: An arrangement (10) for mounting a lens for axial movement comprises a housing (12) defining an axially extending bearing surface (14) and a lens carriage (16) including least three circumferentially spaced bearings (20, 21, 22) in contact with the bearing surface (14) and permitting axial movement of the carriage (16) relative to the housing (12). One of the bearings (20) is biassed towards the bearing surface (14). In use, the arrangement (10) maintains a three-point contact between the lens carriage (16) and the bearing surface (14) despite geometrical variations in the surface.

Abstract: A head-up display system comprising an optical combiner 5 for positioning in front of a pilot's head, in-line with the pilot's normal line of sight and in a plane substantially transverse to said line of sight. Sensor means, comprising a pair of optical sensors 9,10, is arranged to detect motion of the pilot's head towards the combiner 5 and to cause a trigger signal to be generated, prior to impact between the pilot's head and the combiner, if the velocity of said motion exceeds a threshold velocity. Retraction means 7 are coupled to the sensor means for receiving therefrom said trigger signal and are arranged, in response to receipt of said trigger signal, to retract the combiner 5 out of the trajectory of the pilot's head prior to impact between the head and the combiner.

Abstract: An illumination device 1 and methods for producing said device and parts thereof for backlighting a liquid crystal display 3 wherein the illumination device comprises a solid substrate 5 containing at least one groove 11 and an optical fiber 7 comprising an inner core 23 and an outer cladding layer 25 fitted into the groove(s) 11. The outer cladding layer 25 is of reduced thickness on the exposed side of the core 23 such that, light supplied along the optical fiber 7 from a light source 9, is transversely emitted from the optical fiber through the reduced thickness layer 14.

Abstract: A method of monitoring the coalignment of a sighting or surveillance sensor suite including a coaligned laser (18) and sensor (12) includes the steps of: modifying the beam from the laser (18) to render it visible to the sensor (12); and redirecting the modified beam from the laser (18) to impinge on the sensor (12). In the preferred embodiments the frequency of the beam is doubled by a doubling crystal. For certain lasers this renders the beam visible to the human eye, or to a camera.

Abstract: A locking mechanism for releasably locking a rotatable arm 3 to a generally cylindrical axle or wheel 6. The mechanism comprises a slot 7 extending around a region of the axle 6, the slot having first and second abutment surfaces spaced apart in the direction of said movement. A heel member 17, rigidly fixed to the arm 3, projects from the arm into the slot and provides third and fourth spaced apart abutment surfaces 19,27, said third abutment surface 19 being arranged to engage said first abutment surface 18 to prevent rotation of the axle 6 in a first direction. A locking wedge 21 is provided which is moveable between a first release position in which the wedge lies outside the slot 7 and a second locking position in which the wedge projects into the slot to engage said second abutment surface 10 of the slot and said fourth abutment surface 27 of the heel member 17 to prevent rotation of the axle 6 in a second direction opposite to said first direction.

Abstract: A lens mounting arrangement (10) for, for example, an optical telescope, permits movement of the lens from an initial position to an accurately defined first position. The arrangement comprises a track (16) including a first stop (18) at a first end of the track, a lens carriage (12) moveable along the track, and a rotating drive (20) coupled to the lens carriage for moving the lens along the track and into contact with the stop, the stop defining the first position. A coupling (22, 26) is provided between the drive and the lens carriage and includes a resilient link (26) such that the lens carriage may be brought into positive contact with the stop, deformation of the resilient link accommodating excess movement of the drive.

Abstract: The invention relates to a lens mounting suitable for use in a high performance optical instrument. The mounting (10) comprises a body or housing, a linear guide (16; 18; 36; 46; 64) mounted on the body, a lens carriage (14; 34; 44; 62) moveable along the linear guide, and a linear drive, which may be in the form of a ball-screw drive and comprising a ball-screw (20; 80) extending substantially parallel to the linear guide and a ball-screw follower (22; 68) linked to the lens carriage such that rotation of the ball-screw moves the carriage axially along the guide. One or more elements of the ball-screw drive are mounted relative to the linear guide to permit a degree of relative movement therebetween to accomodate misalignment between the linear guide and ball-screw.

Abstract: A head-up display 10 comprises a display device 11 for generating information to be presented to an operator 15 in superimposition with his forward view of the outside world 16, via an off-axis reflectively-powered combiner optic 14 for effecting said superimposition and a relay optic 12, 18 between the display device 11 and the combiner optic 14. The relay optic 12, 18 forms an intermediate image 13 of the displayed information in advance of the combiner optic 14 and the combiner optic 14 collimates the intermediate image for delivery to the operator 15 and re-images the aperture stop formed by the relay optic 12, 18 as an exit pupil at the operator's eye position 20. The relay optic 12, 18 comprises a relay lens 12 and an axis deviation arrangement 18, having a pair of surfaces A, B preferably formed of holograms which are mutually inclined at an acute angle each surface A, B being both transmissive and reflective according to the angle of incidence of light thereon.

Abstract: The method involves directing first and second separate illuminating beams towards a photosensitive film from separate fixed apparent beam source positions respectively in such a manner that the beams are caused to overlap at the point of incidence at the photosensitive film. Stationary interference fringes are generated and the beams are caused to scan in a raster type pattern over the photosensitive film in such a manner whereby overlapping of the beams is maintained throughout the exposure of the film. The apparatus in one embodiment involves the generation of a third illuminating beam which is used to control means to control an associated scanner to effect synchronised movement of the second beam with the first beam. A further embodiment involves memorising the scanning movement of beam in a memory and using the memorised scanning pattern to control the scanner to maintain beam overlap.

Abstract: An optical system for a display having a combiner (1) with a non-conformal reflection hologram and in which an intermediate image (II) of a display source is formed at a location in the light path to and spaced from the combiner (1), the system comprising at least one diffractive element (5,7) disposed in the light path between the display source (2) and the intermediate image (II) and arranged to counter, at least partially, the chromatic dispersion of the non-conformal reflection hologram (1).

Abstract: This invention is concerned with display apparatus of the Head-Up-Display (H.U.D.) type which finds utility in e.g. fighter aircraft. The invention is concerned with providing an H.U.D. which has a profile depth which is substantially and preferably much less than the diameter of the exit lens. The arrangements of the H.U.D. include a cathode ray tube (C.R.T.) display source, a collimating optical means having a plurality of lenses with at least an entrance lens and an exit lens together with a prism and combining means for combining displayed visual information with the view of the scene or object. The prism is so arranged in relationship to the display source that internal reflection of light from the display source within the prism and transmission of light towards the combining means is such as to enable the modular unit profile depth to be between 40% and 60% less than the exit lens diameter.

Abstract: The method involves directing first and second separate illuminating beams towards a photosensitive film from separate fixed apparent beam source positions respectively in such a manner that the beams are caused to overlap at the point of incidence at the photosensitive film. Stationary interference fringes are generated and the beams are caused to scan in a raster type pattern over the photosensitive film in such a manner whereby overlapping of the beams is maintained throughout the exposure of the film. The apparatus in one embodiment involves the generation of a third illuminating beam which is used to control means to control an associated scanner to effect synchronised movement of the second beam with the first beam. A further embodiment involves memorising the scanning movement of beam in a memory and using the memorised scanning pattern to control the scanner to maintain beam overlap.

Abstract: This invention concerns a method and apparatus of using the relatively thin holographic material of a transmission holographic optical element in such a manner whereby a narrow spectral bandwidth may be achieved. The interference fringe planes oriented through the depth of the material are interrogated by way of the edge of the holographic optical element whereby the holographic optical element is caused to respond, in use, in the manner of a relatively thick reflection holographic optical element of considerable effective thickness. The apparatus takes the form of a narrow bandwidth optical filter which is interrogated by a tightly focussed interrogating beam.

Abstract: An imaging device for processing an optical image in the visible and/or infra-red wavelength bands. An optical image receiving area is divided into four segments and each segment is associated with an optical sensing means in the form of a semiconductor chip comprising a plurality of pixels. Each segment also includes a reflection means for reflecting the particular optical image to the associated optical sensing means. The reflecting means preferably takes the form of a reflecting surface within a cube comprising two prisms. The reflecting surface may be fully reflecting dichroic or holographic. A further optical sensing means in the form of a semiconductor chip is employed to the rear of the image receiving areas and is positioned to sense for small separate segments of the four guarter segments in the center of the overall optical image. All the separate received optical images are processed electronically to produce a composite image.

Abstract: This invention is concerned with a thermal imaging optical system finding utility as an individual weapon sight. The system comprises an infra-red objective lens including a chopper blade together with front and back elements with an adjustable element therebetween. Infra-red radiation is received by the objective lens which also incorporates an internal substantially collimated plane polarized visible light source which illuminates a liquid crystal. The path of the infra-red and visible light which is directed to the liquid crystal cell, is repeatedly interrupted by the chopper blade. Changes in the liquid crystal cell due to the infra-red radiation transmitted by the objective lens are caused to modulate the plane polarized visible light transmitted through the liquid crystal cell to generate a visible image. This image passes through a relay inverting system and is detected by a visible light detector and viewed through an eyepiece.

Abstract: Optical viewing apparatus has an obective lens for focussing radiation from a scene or object to form an image on a detector and means for producing a visible display of the image which is viewed through an eye-piece lens. The objective lens is designed to impose a substantial level of barrel distortion on the image and the eye-piece lens imposes a substantial level of pincushion distortion on the observer's view to give improved central resolution. The radiation focussed by the objective lens may be visible or invisible, e.g. infra-red.

Abstract: The article, typically for use in man-made satellites, has high emissivity and low reflectance in the thermal infra-red wavebands between 6 and 30 microns, and also in the visible wavebands. The article is employed either to cover individual solar-cells, thereby protecting the cells from ionizing radiation and micro-meteoroids, and to protect the adhesive bonding the article to the solar cell from u-v light, or as a thermal control mirror to prevent heat build-up. The article has good emissivity in the thermal waveband regions, so the cell can be maintained at a relatively low temperature.

Abstract: An optical substantially afocal beam expander has a negative lens element spaced from a positive lens element. The lens elements are of different materials with respective coefficients of refractive index change with respect to temperature such that the effect of a temperature change on one element is at least partially compensated by the effect of the temperature change on the other element. The beam expander is therefore substantially athermalised with respect to afocality.

Abstract: An interference filter, also referred to as a notch filter, of the type which reflects a certain wavelength range while letting pass over wavelengths bands of a range is disclosed. The filter is designed for operation in the visual and infra-red regions of the electromagnetic spectrum and in the disclosure the uniform layer pairs of material are such that the optical thickness of each layer of the or each layer pair deposited on a plane light-transmitting substrate is a non quarter-wave unequal thickness with respect to its complementary layer. Each layer pair has an overall optical thickness adding up to in total a half-wave thickness.