Headgear with spherical semi-reflecting surface

Claim 1

Headgear for the occupant of a vehicle, incorporating an optical display system, comprising: (A) a member having a concave semi-reflecting curved surface directed inwardly of the headgear and which when the headgear is being worn is at or is movable to a position at which it intercepts the forward line-of-sight of an eye of the wearer; and (B) above the level of the wearer's eyes, an optical projector by means of which luminous data is directed at the aforesaid semi-reflecting surface for reflection thereby to the wearer's eye so that the wearer is presented with a virtual image of the aforesaid luminous data within a predetermined field of view centered on the wearer's forward line of sight; characterized in that the concave semi-reflecting surface is spherical; and (C) the optical projector is secured to the headgear and comprises an extended substantially planar optical data source, and a prism whose shape, dimensions and position are such that rays from all points of the extended planar data source enter the prism at one face thereof, are reflected in the prism downwards to a generally downward and forward facing exit face of the prism, are refracted at the latter face and are then incident on the spherical semi-reflecting surface; and (D) further characterized in that the inclination of the exit face of the prism with respect to the spherical semi-reflecting surface is so chosen that aberration introduced by the prism by virtue of the aforesaid inclination of the exit face is effective to compensate substantially wholly for the aberration introduced by the spherical semi-reflecting surface as a result of the off-axis configuration of the system.