Helmet display systems

A helmet display system including a display arrangement comprising:

• right and left collimating eyepieces;
• and projector means which in operation projects bright data for reflection by the right and left eyepieces to respective right and left eye positions;
• each eyepiece comprising first and second light transmissive/light reflective laminar elements defining a generally downwardly tapering space and defining at a position adjacent the wider end of the tapering space a principal focal plane of the eyepiece which is coincident with a respective one of two image planes formed by the projector means, and each eyepiece being supported at a respective one of two ports of a housing arrangement containing light paths leading from a bright data source of the projector means to the eyepieces by way of an optical system of the projector means including a relay lens and reflective elements serving in operation to direct rays from the bright data source so as to form images at the said two image planes;
• and wherein at at least one of the said ports of the housing arrangement, there is a light transmissive portion of the housing, the lower edge of which is contiguous with the upper edge of the light transmissive/light reflective element of the eyepiece at that port which is remote from the eye position associated with that eyepiece, thereby to extend upwardly the angular range of the field of view available from that eye position;
• and wherein the optical system includes a partially light transmissive, partially light reflective first planar element positioned substantially midway between and above said eyepieces onto which rays for both said eyepieces are directed from said source via a common path, said first element serving to split said rays between a first path which includes a reflective second planar element parallel to said first element to direct the rays through substantially 90 degrees and thence downwardly to the one of the said ports at which said transmissive portion is located and a second path which includes reflective third and fourth planar elements in parallel spaced relation in planes at right angles to the plane of said first element to direct the rays through two successive turns of substantially 90 degrees in the opposite sense and thence downwardly to the other one of said ports;
• and wherein said rays for both said eyepieces are incident on said first element in a direction substantially parallel to a straight line joining said eyepieces for passage along said first path after transmission through said first element and passage along said second path after reflection by said first element.