Abstract: A head up display system 10 comprises an image generator 11 supported and boresighted within a cockpit. The system 10 includes a housing 13 to support the generator 11 and a holographic combiner 14 which is upstandingly supported on top of the housing 13. In operation, the generator 11 forms an image at object surface 17 and a relay lens arrangement 16 receives, collimates and conveys the image along an optical pathway 19 and through an exit pupil 18. A prism 20 and a mirror 21 are arranged along the pathway 19 to fold the pathway 19 from a generally horizontal direction to a generally vertical direction towards the combiner 14.

Abstract: A method of producing a reflection hologram wherein light from a source (29) is directed onto the hologram recording medium (23) via a lens (21) which causes light reaching the medium (23) to pass through a construction point (33). The light beam is arranged where it is incident on the lens (21) to be of small cross-sectional area compared with the lens aperture and is arranged to scan over the lens aperture so that the beam scans the medium (23) in a regular pattern of overlapping narrow bands. In this way the hologram may be made to have uniform spectral properties despite a non-uniform energy distribution in the beam.

Abstract: A method and apparatus for making reflection holograms wherein a film (27) of light sensitive material in which the hologram is to be formed is rotated about a first axis (Y--Y) which is itself rotated about a second axis (X--X) which intersects the first axis at a position (Z) spaced from the film so that a coherent light beam (29), which is directed onto the film and whose axis passes through the point of intersection of the axes, scans the film in a pattern of overlapping narrow bands. The bands may be rectilinear or circular.

Abstract: A color selective filter in the form of a holographic reflector is produced by a method which includes the step of exposing a photosensitive film of gelatine to a monochromatic laser beam. In order to obtain acceptably short exposure times and to enable substantially the whole of the available laser light to be utilized, a relatively narrow laser beam is sequentially scanned across the surface area of the gelatine film in a scanning pattern which consists of a large number of parallel straight lines. The diameter of the laser beam spot is very large as compared with the spacing between adjacent line scans. In this way each point on the gelatine film is scanned a very large number of times.The laser beam 8 is generated by a laser 7 and deflected by two movable mirrors 10 and 11, which are controlled so that the beam scans the whole of the gelatine film 1.