Opto-mechanical semi-diameters (OMSDs) provide the OpticsViewer user with greater flexibility when generating opto-mechanical features outside the clear aperture of the lens. This feature offers a comprehensive way to model realistic lens apertures with opto-mechanical semi-diameters and is especially useful for complex lens systems.
Authored By Thomas Pickering
In order to comprehensively model realistic optical systems, OpticsViewer allows the user the ability to work with opto-mechanical semi-diameter (OMSD) properties. There are two surface parameters that allow the user to generate the features typically found outside of the clear aperture of a lens: Chip Zone and Mechanical Semi-Diameter. Through these two parameters, opto-mechanical semi-diameters are available in multiple editors.
Within the Lens Data Editor (LDE), there are two parameter columns: Chip Zone and Mech Semi-Dia (the mechanical semi-diameter). The Chip Zone extends the non-traceable semi-diameter and continues the current sag curve of a given surface. Mech Semi-Dia adds a non-traceable unique structure to the surface and extends the semi-diameter with a flat surface. These parameters are supported for all rotationally symmetric surface types as well as Irregular and Zernike surfaces. The effects of the two parameters are shown below.
The portion of the surface defined by the Clear Semi-Diameter, i.e. the 'effective aperture’ of the surface, is the region over which the surface is polished, coated and tested. The Chip Zone is the immediate region outside the testable zone. It follows the same curve as the testable region, is not testable and typically will not conform to optical specification. The global Clear Semi-Diameter Margins can still be set in the System Explorer but can also be turned off individually in Surface Properties...Aperture.
In the first figure, the Mechanical Semi-Diameter was fixed at 6 mm to demonstrate the effect of the parameter. By default, however, the Mechanical Semi-Diameter is set to the Automatic Solve. This results in a value that is calculated to be equal to the sum of the Clear Semi-Diameter and the Chip Zone values. If the surface forms part of a lens, the "Squared to Next Surface“ option may be selected so that the Mechanical Semi-Diameter is extended to provide the "square" edge explicitly. In the image below, Surface 2 has "Squared To Next Surface" selected which has added 0.536 mm of flat surface in order to extend the lens past the Chip Zone.
Once a circular aperture is defined for a surface, the Clear Semi-Diameter is no longer a relevant parameter. The Chip Zone and Mechanical Demi-Diameter are then built upon the Circular Aperture:
Rays will only be allowed to trace through the aperture defined by the Clear Semi-Diameter. Any additional apertures will restrict the light further. However, no rays will trace through the Chip Zone or Mechanical Semi-Diameter region and a ray trace error will be reported for any invalid rays.
Chip Zone and Mechanical Semi-Diameter are also correctly exported into the ISO Element Drawings. It is important to note that all of the surface values are not read into the settings immediately, but the analysis is indeed using the correct values in generating the drawing. If you want to see the values in the settings, you simply hit the “Reset from LDE” button. You can manually change the values by de-selecting the “Automatic” checkbox. All values are editable to allow you to generate different XML files corresponding to different lens geometries that could be used to obtain different quotes from the Cost Estimator without having to actually modify the lens in the LDE.
The Chip Zone and Mechanical Semi-Diameter parameters have matching Multi-Configuration Editor (MCE) operands: CHZN and MCSD respectively. In this way, two different opto-mechanical semi-diameters can be visualized in Layout plots. Shown below are two possible configurations with both displayed in a 3D layout.
There are three operands in the Merit Function Editor (MFE) that correspond to the Mechanical Semi-Diameter parameter: OMSD, OMMI, and OMMX.
The OMSD operand simply reports the value of the Mechanical Semi-Diameter parameter of the specified surface. The OMMI and OMMX operands constrain the Mechanical Semi-Diameter values to be larger or smaller than the specified target. With them, you can control multiple surfaces simultaneously, specified by the range between "Surf1" and "Surf2". In addition, many other operands, including all edge thickness operands (e.g. ETVA, MXEG, MNEG, …), have a Mode flag. This allows the user to optionally consider or ignore the Chip Zone and Mechanical Semi-Diameter when computing the operand values.
Irregular and Zernike Standard Sag surfaces support the opto-mechanical semi-diameter. Therefore, when tolerancing surface irregularities (i.e. TIRR and TEZI), decenters and tilts (e.g. TIRY), OMSD values will get carried forward. The value for TIRX and TIRY is given with respect to the clear aperture. Similarly, the TEZI normalization is over the clear aperture.