Fresnel lenses are constructed such that the curved surface of a lens is
collapsed in annular zones to a thin plate. As shown in the figure below, this
has the refracting effect of the lens without its thickness or weight.
Such lenses are often used as condensors in overhead projectors, spotlights
and signal lamps.
The annular facets are modelled exactly in OpTaliX. Thus, various depths of the
annular facets in a Fresnel lens lead to different aberrations. Fresnel
surfaces can be refracting, reflecting, aspheric and decentered/tilted. The may also be
grouped in arrays