Head up displays using optical combiner with three or more partially reflective films

Claim 1

A display unit for a head up display system for use in a vehicle comprising: an optical projector which projects, collimated, from an output aperture, optical data presented by a source; and an optical combiner comprising partially light transmissive, partially light reflective means so located with respect to said output aperture that, in use, an observer viewing a distant real world scene by transmission of light through said means sees optical data projected through the output aperture, after reflection at said means, as a virtual image superimposed on the distant scene and including the improvement that the output aperture of the optical projector is of generally rectangular shape and said optical combiner comprises: a body of light-transmissive, refractive material having first and second substantially optically flat parallel external surfaces which face respectively, forwardly, towards the distant real world scene and rearwardly, towards the observer, in use of the unit; within said body, at least three substantially optically flat and parallel films supported and separated by the material of the body and effective to reflect light incident thereon from the optical projector and to transmit light incident thereon from the real world; and a third external surface through which optical data from said projector enters said body for subsequent reflection at said films towards the observer, said third external surface making with said films an angle equal to the angle between the films and said second surface, and said films being relatively positioned so that, observed in the observer's viewing direction to the distant scene, each said film provides a different field of view of the projected optical data.