Fresnel

The Fresnel surface model is used to simulate flat surfaces which have been etched to have a spherical (or optionally aspheric) profile on a small scale (for Fresnel lenses which are not flat see the extended Fresnel surface type description). The surface intercept is determined by computing the intersection of the incoming ray with a plane. Once the plane intercept points are found, the surface is then treated as generally curved for the purposes of refraction into the next medium. This is only an approximation to a real Fresnel lens, however. The real Fresnel lens has grooves which may alter the exact intercept point. The model used here is adequate for Fresnel lens which have fine grooves (the groove depth is very shallow compared to the aperture). Extreme Fresnel lenses, such as those used in lighthouses, are not modeled well. The radius of curvature and conic constant, if any, are specified in the same manner as a Standard surface. The parameter values are exactly the same as for the even asphere model; polynomial aspherics are supported to 16th order.

For other types of Fresnel surfaces, see "Extended Fresnel" and "Generalized Fresnel".

PARAMETER DEFINITIONS FOR FRESNEL SURFACES

Parameter #	Definition
1 - 8	α1 - α8

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