Lens Module Including Two Lens Elements Separated by an Air Gap

A head-mounted display may include a display system and an optical system that are supported by a housing. The optical system may be a catadioptric optical system having a removable lens element and a non-removable lens element. The optical system may include a quarter wave plate that is coated to the non-removable lens element without an intervening adhesive layer. The optical system may further include a reflective polarizer and a linear polarizer. The removable lens element may be selectively attached to the optical system. The removable lens element may be separated from a non-removable lens element by an air gap when the removable lens element is attached to the optical system. The removable lens element may have a convex curved surface that conforms to a concave curved surface of the non-removable lens element.