Projection lens with four glass elements having spherical surfaces

Abstract

A projection lens can include four lens elements, each lens element being formed from glass and including spherical or planar incident and exiting surfaces. Compared to a projection lens that uses three lens elements, the four-element projection lens has relaxed manufactured and alignment tolerances. Unlike a projection lens that uses one or more plastic elements or uses aspherical surfaces, the all-glass projection lens can be manufactured using relatively fast and inexpensive grinding and polishing techniques. One or two of the glass lens elements can optionally be formed symmetrically, so as to be reversible. One glass element can optionally be piano-convex. A right-angle prism can direct light from a video display into the four glass elements. An achromatic prism can angularly divert the optical axis by about eight degrees and can direct light out of the four glass elements into a near-eye waveguide.