Annular Aspheric Lens
The annular aspheric lens is an annular solid with a conic asphere with even aspheric polynomial terms to 16th order, identical to the Even Asphere Lens object, on both front and back faces. See "Even Asphere Lens" for a description of the even aspheric polynomial.
The annular shape is defined by a min and max radial aperture which may be different on the front and back faces. The aspheric rear face is offset from the front by a thickness measured at a specified radial aperture, which may be zero.
That thickness is called "Thickness Aperture" and it tells the radial distance at which the object thickness is defined.
For example, the below picture shows two cross-sections of an Annular Aspheric Lens where Maximum Front Radial Aperture = Maximum Back Radial Aperture = 20 mm and Minimum Front Radial Aperture = Minimum Back Radial Aperture = 10 mm.
- If the Thickness Aperture = 10 mm, then the object thickness is defined at a radial distance of 10mm.
- If the Thickness Aperture = 20 mm, then the object thickness is defined at a radial distance of 20mm.
For backward compatibility with the original definition of this object, the back face parameters are listed before the front surface parameters.
The following restrictions apply: all apertures must be positive, maximum apertures on each face must be larger than the minimum aperture on that face, and if one face has zero for a minimum aperture the other face must also have a zero minimum aperture.
The object is defined by the following parameters:
| Parameter # | Description | Face Name | Face # |
| 1 | Minimum Front Radial Aperture | Front | 1 |
| 2 | Maximum Front Radial Aperture | Front | 1 |
| 3 | Minimum Back Radial Aperture | Back | 2 |
| 4 | Maximum Back Radial Aperture | Back | 2 |
| 5 | Thickness Aperture | Side | 0 |
| 6 | Back Face Radius of Curvature | Back | 2 |
| 7 | Back Face Conic | Back | 2 |
| 8 | Thickness (measured at the Thickness Aperture) | Side | 0 |
| 9 -16 | Even Aspheric coefficients α1 through α8 for the back face | Back | 2 |
| 17 | Front Face Radius of Curvature | Front | 1 |
| 18 | Front Face Conic | Front | 1 |
| 19 - 26 | Even Aspheric coefficients α1 through α8 for the front face. | Front | 1 |
| 27 | The Radial Aperture to the edge of the front side of the lens. | Side | 0 |
| 28 | The Radial Aperture to the edge of the rear side of the lens. | Side | 0 |
Face Numbers: Outside face connecting the "maximum" apertures Face 0, front face Face 1, back face Face 2, inside face connecting the "minimum" apertures on the front and back Face 3.
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