A detailed description of the design of a plastic, aspheric Fresnel lens on a spherical surface is provided. The design technique is based on calculating solutions to Snell’s law along the lens surface. These lenses were intended for the wavelength range of 8 to 12?m. However, the method easily applies to lenses designed for other wavelengths. The procedure used to manufacture the lenses is to construct a diamond-turned master surface, followed by injection molding with highdensity polyethylene.