Grid Sag Lens 2
The Grid Sag Lens Front/Back is a solid volume object that supports two Grid Sag surfaces for the front and rear faces. For a detailed description of the sequential Grid Sag surface shape, see the sequential surface " Grid Sag ". Data provided in the grid sag files is applied on top of an aspheric substrate for each face. The substrate shapes are defined via a radius of curvature, a conic constant, and 8 aspheric coefficients (which are used to define an even aspheric geometry of up to order r16). The grid data on each face can be decentered in X and Y relative to the aspheric substrate for that face. These decenters are applied after any tilts or decenters are made to the substrate.
Grid Sag Lens Front/Back objects use the following parameters:
| Parameter # | Description | Face Name | Face # |
| 1 | The x half width in lens units (see discussion below). | NA | NA |
| 2 | The y half width in lens units (see discussion below). | NA | NA |
| 3 | The front surface radius of curvature in lens units. | Front | 1 |
| 4 | The front surface conic constant. | Front | 1 |
| 5-12 | The front surface αi aspheric coefficients. See Grid Sag for details. | Front | 1 |
| 13 | The front surface interpolate flag, for specifying the interpolation method used in calculating the data grid portion of the surface sag at any arbitrary point: Use 0 for bicubic and 1 for linear. | Front | 1 |
| 14 | The front surface decenter in X, in lens units. | Front | 1 |
| 15 | The front surface decenter in Y, in lens units. | Front | 1 |
| 16 | The front surface tilt about X, in degrees. | Front | 1 |
| 17 | The front surface tilt about Y, in degrees. | Front | 1 |
| 18 | The front surface tilt about Z, in degrees. | Front | 1 |
| 19 | The front surface order flag, which defines whether tilts should be applied before or after decenters (acts just like the order flag for coordinate break surfaces in sequential mode). | Front | 1 |
| 20-21 | The front surface X- and Y-decenter values for the grid data, in lens units. This is the decenter of the grid data relative to the tilted and decentered aspheric substrate. The decenter values are added to any decenter values defined in the GRD file (which is also applied to the tilted and decentered substrate). | Front | 1 |
| 22 | The axial lens thickness in lens units. This value defines the thickness from the nominal surface vertex of the front face (i.e. before tilts and decenters) to the nominal surface vertex of the rear face. | Side | 0 |
| 23 | The rear surface radius of curvature in lens units. | Back | 2 |
| 24 | The rear surface conic constant. | Back | 2 |
| 25-32 | The rear surface αi aspheric coefficients. See Grid Sag for details. | Back | 2 |
| 33 | The rear surface interpolate flag, for specifying the interpolation method used in calculating the data grid portion of the surface sag at any arbitrary point: Use 0 for bicubic and 1 for linear. | Back | 2 |
| 34 | The rear surface decenter in X, in lens units. | Back | 2 |
| 35 | The rear surface decenter in Y, in lens units. | Back | 2 |
| 36 | The rear surface tilt about X, in degrees. | Back | 2 |
| 37 | The rear surface tilt about Y, in degrees. | Back | 2 |
| 38 | The rear surface tilt about Z, in degrees. | Back | 2 |
| 39 | The rear surface order flag, which defines whether tilts should be applied before or after decenters (acts just like the order flag for coordinate break surfaces in sequential mode). | Back | 2 |
| 40-41 | The rear surface X- and Y-decenter values for the grid data, in lens units. This is the decenter of the grid data relative to the tilted and decentered aspheric substrate. The decenter values are added to any decenter values defined in the GRD file (which are also applied to the tilted and decentered substrate). | Back | 2 |
If the x and y half widths are zero, the lens shape is rectangular and the size is defined by the data in the GRD file. If the x half width is zero, and the absolute value of the y-half width is not zero but is less than the size of the data in the GRD file, then the part is square (if the y half width is greater than zero) or circular (if the y half width is less than zero). If both the x half width and the y half width are not zero, and the absolute values of both half widths are less than the size of the data in the GRD file, then the part is rectangular (if both half widths are positive) or elliptical (if either half width is negative).
The actual point by point sag data is defined by placing the data in a properly formatted files ending in the extension GRD. The file format is defined in the "Importing grid data" section of the " Grid Sag " sequential surface section of the Help Files. The grid data files must be placed in the folder <objects>\Grid Files. The file names, without the path, are specified via combo boxes on the NSC Object Properties dialog box.
The reference coordinate is the center of the front face. Face Numbers: Side faces Face 0, front face Face 1, back face Face 2.
In constructing Grid Sag Lens 2 objects, some care should be taken to avoid creating geometries where the front and back surfaces overlap. Because of the complex combination of the thickness parameter, the front/rear substrate geometries, and the front/rear sag grids, OpticStudio may not generate a warning message for some invalid geometries. In these cases, errors may only be detected during a ray trace.
Next: