An optical system for displaying a magnified virtual image of an image emitted by a display to a viewer. The optical system includes first and second lenses facing each other and spaced apart by an air gap to define an optical cavity therebetween. The optical cavity includes a reflective polarizer disposed on a major surface of the first lens, and an optical stack disposed on a major surface of the second lens. The optical stack includes an absorbing polarizer, a first retarder layer, a partial reflector, and a second retarder layer disposed between the absorbing polarizer and the partial reflector. The first and/or second lenses is/are birefringent lens provided outside the optical cavity to control polarization.