“…The layouts of the objectives are extremely diverse and strongly depend on the type of image generator being used, its lighting layout, the purpose of the system, its angular field, etc. The optical layouts can be either traditional axisymmetric systems or systems that use decentered elements and elements with no axial symmetry, 4,6,7,21,[23][24][25][26] including off-axis mirrors. Optical systems for helmet-mounted and cabin-type displays, both projection and collimator type, are evolving in the direction of simpler design, reduced fabrication cost, smaller dimensions, and enhanced image quality.…”