Fresnel effects refer to the relationship between the angle of incident light, the angle of the surface and the angle to the viewer (ie, the angle that light bounces from the light source, off the surface, and to the viewer). There are materials which will reflect light differently based on the angle. Some surfaces will only reflect certain color bands depending on the angle. Other surfaces only change what we call highilght, shininess based on angle. Other surfaces have different strengths of reflection based on angle. The Fresnel lens is a simple lens that can transmit light focusing a wide point source into a single beam using a material (like glass) of the same refaction index. This was really important a long time ago because people needed lenses that would produce beams for light houses from a bulb (or fire). You could do this with a Fresnel lens and construct it rather easily. Lenses like the camera lenses we have now which have smooth rounded continuous surfaces are actually a serious challenge to construct (especially if they have to BIG). So Fresnel lenses are simple layered "steps" of glass that are in stages to coarsely represent the smooth like lens we can make now. -Kix

-Kix