Abstract: An optical system mounted on a helmet (29) for superimposing a collimated image of a display object on the external view of the helmet's wearer comprising: display object means (1a, 1b) mounted on the helmet for generating a display; a concave collimator (6a, 6b) for collimating light from said display; an optical relay unit (3a, 3b) located in the forehead region for generating an intermediate image of said display in the focal plane of the collimator; a reflecting surface (4a, 4b) for reflecting display light from the relay unit towards the collimator; and an inclined combiner (5) essentially transparent to incoming display light and to the wearer's external view, for reflecting display light reflected from the collimator towards the viewer's eye.

Abstract: A cathode ray tube comprising a cathode (K) for emitting a beam of electrons; a grid (G) for controlling the intensity of the beam; three or more anodes (A1, A3, A4); a control for varying the potential of at least one of the anodes (A3) for focusing the beam to form a spot on a screen; and an additional, dynamic focus electrode (A2) maintained generally at a potential close to the cathode/grid potential. Suitable structure may be included for applying to said dynamic focus electrode a high frequency signal to provide a rapid focus control. Said dynamic focus electrode may comprise a plurality of circumferentially disposed segments and including applying a separate high voltage to each segment thus allowing the possibility of creating a quadruple action in conjunction with at least one adjacent electrode, said segments covered with a deposited high-resistance conducting film to prevent charging effects.

Abstract: An EHT power supply, for example for a cathode ray tube, having a voltage multiplier of a multi-stage Cockroft-Walton type, in which the capacitors of each stage are formed by layers of conducting material juxtaposed on either side of a layer of dielectric material, the layers of dielectric material forming an integral part of the mechanical structure of the multiplier and physically supporting the rectifier diodes of the multiplier. In one embodiment of the invention, the multiplier is formed as a closely-spaced stack in which each stage comprises a separate layer of dielectric material, and in another embodiment the capacitors of the AC side of the multiplier are formed on one layer of material and the capacitors of the DC side of the multiplier are formed on another layer, the two layers being disposable on opposite sides of the neck of a cathode ray tube with the successive stages being longitudinally disposed along the neck.

Abstract: A low-cost head-up display suitable for automobiles consists of a transmitting diffractive element (3) located below an observer's line of sight for diffracting light from an information display (2)onto a combiner glass or the windscreen (1) of the automobile, and an opaque mask (4) positioned close to the diffractive (3) element so that specular reflections from the display (2) are screened from the observer's field of view.

Abstract: The gun comprises a cathode, a control grid, a first anode a second anode and a third anode. Preferably a beam width limiting aperture is provided in the first anode. In one example the current modulating voltage applied to the grid is 0 to -50V, the voltage applied to the first anode is +5 kV, the focus voltage applied to the second anode is +500V, and the EHT voltage applied to the third anode is +25 kV. A main focussing lens is formed by the second and third anodes, but the spacing of the first and third anodes is small so that the focussing effect is also substantially dependent on the voltage of the first anode. The field strength between the grid and first anode is high, which combined with the high first voltage produces a small crossover.

Abstract: An optical system for a head-up display for example for producing a collimated image of a crt display on the external view of an aircraft pilot includes an optical relay unit including two elements (11,12) to produce a double fold in its optical axis to reduce the physical size of the relay unit. One of the two units (11), preferably of a diffractive type, is adapted to transmit light of the display color at a first angle of incidence and to reflect such light at a second angle of incidence.By use of a diffractive element having a narrow band reflectance, the system is extended to include embodiments for combining the display of two different color displays and a full color version using three crts is described.

Abstract: In a display system light from an object (14) is deflected on to a collimator (16) and superimposed on an external view through a combiner (10) from an observing position (11). Relay optics (17) in the path of light from the object (14) has spaced apart elements (L.sub.1,L.sub.2) which produce first and second exit pupils (P.sub.1, P.sub.2). Exit pupil volumes (V.sub.1, V.sub.2) overlap to give an extended field of biocular view. The restricted field of view associated with prior art display systems is overcome since the present system provides a large field of view at the observing position (11), while system components fit within aircraft space constraints, such as windshield (19), fairing (33) and ejection line (20). Space remains available for other instrumentation, such as a second display CRT (45).

Abstract: A head up display system including a light emissive object at an object plane and a collimator and combiner to provide a collimated image for viewing at an eye plane overlaid on a view through the combiner. The object emits light in at least two chromatically separated emission wavebands and by a diffractive optical element in the light path from object plane to eye plane having narrow band reflection characteristics at each emission wavelength.