Sagging a Lens Surface into Zones
The Fresnel lens had its origin in the design of lighthouse lenses. Its grooved surface represented a novel method for substantially reducing the amount of glass needed to produce large aperture, short focal length elements. Surface shapes derivative to the Fresnel lens find application in general illumination as well as in imaging systems such as cameras and telescopes. Their design is based upon annular zones which can either have constant width or occur at radii associated with a fixed sag amount as shown in Figure 1. The objective of this article is to provide FRED users with a tool for the creation of Fresnel surfaces until such time as it becomes a permanent member of FRED’s native element library.