Helmet supported optical systems with four reflections

Claim 1

A helmet supported optical system which provides an eye of a wearer of a helmet with a direct view of the scene forward of the wearer on which is superimposed collimated optical imagery, said system comprising: an eyepiece comprising a body of light refractive material, supported with respect to the helmet in front of a position for said eye defined with respect to helmet axes, having: a light input face; a boundary surface opposite said input face; substantially flat and parallel fore and aft faces; and, internally of said body bridging the space between said input face and said boundary surface, an aerially extensive region concavely curved towards said aft face and possessing both light reflective and light transmissive properties; and means supported with respect to the helmet operable to develop a bright data representation at a plane substantially congruent with the principal focal plane of said aerially extensive region and defined with respect to said input face of the eyepiece such that light from said bright data representation developed at said plane entering said eyepiece at said input face is: internally reflected forwardly toward said aerially extensive region; partially reflected by said aerially extensive region rearwardly towards said aft face; and transmitted through said aft face to the said position for said eye, wherein between said means operable to develop said bright data representation and said input face of the eyepiece, there is a second body of light refractive material having: a first face by way of which light from said bright data representation can enter said second body; a second face having a mirror coating; and a third face confronting said input face of the eyepiece, the conformation of said second body of light refractive material being such that rays from said bright data representation entering said second body at said first face are: reflected at the mirror coating on said second face back to the said first face such that they are incident on said first face at angles greater than the critical angle of said second body to air; are totally internally reflected at said first face to said third face; and transmitted through said third face to said input face of the eyepiece.