US Patent 10222614 Head-up display and vehicle

A refractive optical system is disposed in an optical path from a display surface to a viewing area and between a projection optical system and the viewing area. A housing receives a display device, the projection optical system, and the refractive optical system, and is provided with an opening. An opening cover has at least partially a curved portion, and is disposed in the opening so that light emitted from the display surface is incident on a convex side of the curved portion. When a light beam that is emitted from a center of the display surface and reaches a center of the viewing area is referred to as a reference light beam, a head-up display satisfies the following condition (1):L2≤L1  (1)