Abstract: Headgear incorporating an optical display system comprising, an optical data source mounted within the headgear above the level of the wearer's eyes, an image combiner having a spherical reflecting surface directed inwardly of the helmet and intercepting the wearer's forward line-of-sight, and a prism positioned and dimensioned so that a collimated, aberration free virtual image of the data source is presented to the wearer as a result of reflection of rays transmitted from the data source by way of the prism to the spherical reflector. Such aberration as is introduced by the prism compensates for aberration introduced by the spherical reflector.