Biocular viewers permit magnification of small areas without optical distortion and produce an image that can be viewed with both eyes. Current applications range from biocular viewing of driftsights, image intensifiers, or FLIR displays while in a moving vehicle, to quick scanning of reconnaissance imagery in ground based photointerpreter facilities. Other potential applications include allowing the use of space-saving devices available only in small formats, such as liquid crystal video displays. Advantages include absence of facial contact, no diopter adjustment necessary, operator may wear glasses incorporating astigmatic corrections, and wide angle viewing (45-degree field of view) to allow correct perspective presentation. The lack of distortion reduces eye fatigue and reduces the likelihood of nausea while viewing in an unstable environment. Distortion inherent in certain image intensifier tubes can be partially corrected with a biocular viewer.
Herman G. Eldering,
"Application Of Biocular Viewers To Airborne Reconnaissance", Proc. SPIE 0496, Airborne Reconnaissance VIII, (11 December 1984); doi: 10.1117/12.944406; https://doi.org/10.1117/12.944406