Fresnel 2
This object is an idealized Fresnel lens. Unlike the Fresnel 1, this Fresnel lens uses the approximation that the Fresnel faces are infinitesimally small, and may be ignored for purposes of computing the ray-object intersection point. Unlike the idealized Fresnel surface in sequential ray tracing (see "Fresnel"), this object does not add or subtract any phase to the ray.
The substrate shape is either a flat disk or a rectangle. The front face of the substrate consists of a radial or cylindrical Fresnel lens. The radial profile is defined by a sag expression identical to the Even Asphere surface:
If the Fresnel surface is cylindrical, then the profile is described by an identical expression in the y coordinate alone:
The Fresnel lens may be either radial or cylindrical independent of the substrate shape. It is possible to define a radial Fresnel on a rectangular substrate or a cylindrical Fresnel on a radial substrate if desired.
The Fresnel 2 object is defined using these 14 parameters:
| Parameter # | Description | Face Name | Face # |
| 1 | Radial Height. This is the maximum radial aperture of the lens if radially symmetric, or the y half height if cylindrically symmetric. | NA | NA |
| 2 | X Half Width. This is the half width of the lens if cylindrically symmetric. If this parameter is zero, then a rotationally symmetric lens is generated. | NA | NA |
| 3 | Thickness. The thickness of the Fresnel in lens units. This value must be positive. | Side | 0 |
| 4 | Is Cylinder? If zero, the Fresnel surface will be radial, otherwise, the surface will be cylindrical. | Side | 0 |
| 5 | Radius. The base radius of curvature. This is one over the value "c" in the sag expressions above. | Front | 1 |
| 6 | Conic. The conic constant "k" in the sag expressions above. | Front | 1 |
| 7-14 | The coefficients on the even radial powers of r if "Is Cylinder" is zero, otherwise these are the coefficients on the even radial powers of y. Note these coefficients have units as y and r are not normalized. | Front | 1 |
Because the object is a closed volume, it may be reflective, refractive, or absorbing.
The reference coordinate is the center vertex of the side of the lens with the Fresnel faces. Face Numbers: Front face Face 1, back face Face 2, all other faces Face 0.
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