The poly lenses we use (index 1.586) are formed by putting the material into a mold. We then cut a curve into the back of the lens with a type of specialized cnc machine. The front, however, still has distortions of the front of it from the molding proess. This is especially easy to see with polarized lenses. A property of a lens materials is Abbe value. The Abbe value is a measure of the degree to which light is dispersed when entering a lens. (Dispersion occurs when white light is broken into its component colors, like a prism hanging in a window.) The lower the Abbe value, the greater the dispersion of light, causing chromatic aberration (color fringing) in the periphery of the lens. The higher the Abbe value, the better the peripheral optics will be. A lower Abbe value means that the lens will have more chromatic aberration. Standard plastic has an Abbe value of 58. Most high index materials have a much lower Abbe value of 36 although Spectralite high index has an Abbe of 47.

Sean