Diffractive optics
Diffractive optics (DO) are used in lens designs that would otherwise require large and heavy chunks of glass. DO lenses, compared to non-DO lenses of similar focal length and aperture values, are usually smaller and lighter. In addition, DO lenses have superior chromatic aberration suppression characteristics that allow for sharper photographs; the chromatic aberration produced by DO lenses is opposite in direction to that produced by refractive lenses, and so the coupling of a diffractive element and a refractive element can effectively cancel chromatic aberration.