Aspheric V Double aspheric
Aspheric lens options can further reduce thickness by creating a more complex lens surface which isn't completely round (i.e. spherical like a globe). Flatter curves are created which gradually change over the lens surface. This can be done on one side of the lens (Aspheric), or both sides of the lens (Double Aspheric) - the latter double option being the thinnest and lightest.