Airborne map displays have been in use for over 30 years. Over this period they have evolved from directly viewed paper maps to extreme optical systems projecting a combined image of a film based map and a Cathode-Ray-Tube (CRT). In the Horizontal Indicator used in the F13 Hornet, a magnified image of the map is formed on a screen. The screen image and the CRT display are then combined and reimaged within a restrictive space envelope using a high aperture (F/0.8), wide field (75°) inverse telephoto transfer lens. At this second image plane a field lens produces a real exit pupil at the pilot's head position. This system arrangement maximises the image brightness yet minimises the effect of high ambient illumination washing out the display. Greater resolution was required for a vehicle based Map/CRT display. This prevented the adoption of any optical system using intermediate screen images. A conventional system employing a double Gauss relay lens and binocular Erfle eyepieces was adopted.
David G. Norrie, David G. Norrie,
"Optical Systems For Use In Combined Map And Cathode-Ray-Tube Displays", Proc. SPIE 0237, 1980 International Lens Design Conference, (16 September 1980); doi: 10.1117/12.959124; https://doi.org/10.1117/12.959124