Helmet systems

Claim 1

A helmet system comprising a helmet (11) and, carried by the helmet (11), an optical arrangement (13) incorporating: an eyeplece (15 or 50) having a rearwardly facing, concavely curved, first element (21 or 59) exhibiting substantial reflectivity to light within a narrow visible waveband and substantial transmissivity to visible light other than that within the said visible waveband; an aerially extensive bright-image-forming source (17 or 67) emissive of light within said visible waveband; and between said source (17 or 67) and said eyepiece (15 or 50), an optical relay arrangement (19 or 63, 65) including an inclined reflector (29 or 63) operable to fold rays of light emitted by said source (17 or 67) within said visible waveband for incidence with said eyepiece (15 or 50), said optical relay arrangement (19 or 63, 65) per se and the position of said optical relay arrangement (19 or 63, 65) relative to said source (17 or 67) and said eyepiece (15 or 50) being such as to form an intermediate real image (P or P1) of said source (17 or 67) substantially coincident with the principal focal plane of said first element (21 or 59), whereby said source (17 or 67) appears at an eye position (E or E1) defined by said helmet (11) in the line-of-sight through said eyepiece (15 or 50) as a virtual image at infinity, characterised in that: said inclined reflector (29 or 63) is substantially transmissive to infrared radiation within an infrared waveband; said eyepiece (15 or 50) incorporates a second rearwardly facing concavely curved element (31 or 61) which is substantially reflective to infrared radiation within said infrared waveband and substantially transmissive to visible light; there is located on the side of said inclined reflector (29 or 63) remote from said eyepiece (15 or 50) an aerially extensive sensor (37 or 72) operable to develop an electrical output representative of the position of incidence within a sensing area of the sensor (37 or 72) of infrared radiation, within said infrared waveband, brought substantially to focus on said sensing area; and there is substantially coincident with the principal focus of said second element (31 or 61) an infra-red source (35 or 71A) emissive of infrared radiation within said infra-red waveband, the arrangement being such that when said system is in use with an eye located at said eye position (E or E1), infra-red radiation from said infra-red source (35 or 71A) is reflected collimated by said second element (31 or 61) through said eyepiece (15 or 50) to said eye position (E or E1), partially reflected by said eye at said eye position (E or E1) and brought substantially to focus at a position within the sensing area of said sensor (37 or 72), said position corresponding to the angular position of said eye with respect to helmet axes.