Optical System Design for a Head up Display Using Aberration Analysis of an Off axis Two mirror System
This study presents a new optical system for a combiner type head up display (HUD) with a cylindrical lens as an asymmetrical aberration corrector, instead of a freeform mirror. In the initial design process based on off axial aberration analysis, we obtain an off axis two mirror system corrected for linear astigmatism and spherical aberration by adding a conic secondary mirror to an off axis paraboloidal mirror. Thus, since the starting optical system for an HUD is corrected for dominant aberrations, it enables us to balance the residual asymmetrical aberrations with a simple optical surface such as a cylinder, not a complex freeform surface. From this design process, an optical system for an HUD having good performance is finally obtained. The size of the virtual image is 10 inches at 2 meters away from a combiner, and the area of the eye box is 130x50 mm2.