Abstract: Embodiments described herein provide an optical system having a light source (e.g., LED) and a high numerical aperture multi-element optical stack. According to one embodiment, the optical stack can reimage an entrance aperture. The multi-element optical stack can include a number of optical elements forming a series of lenses. The series of lenses comprises, a first lens positioned to receive light emitted in a first beam angle and a second lens more distal from the LED than the first lens, the second lens defining a second lens exit aperture that has at least a minimum area necessary to conserve radiance for the emission beam angle in air. The lenses in said series of lenses are configured, in combination, to successively reduce a beam angle of light from the first beam angle to the emission beam angle.