US Patent 10495877 Free-form surface lens and head-up display

Head-up display includes display device and projection optical system. Display device displays an image. Projection optical system includes refraction lens. Projection optical system projects the image displayed on display device to an observer. Refraction lens is disposed while inclined with respect to a reference beam. An incident surface of refraction lens is a concave surface relative to a side of display device in an X-axis direction. A curvature in a Y-axis direction of the incident surface is smaller than a curvature in the X-axis direction.