Modeling optics with realistic edge apertures

Opto-mechanical semi-diameters (OMSD’s) provide the OpticStudio 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, OpticStudio 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 Sequential and Non-Sequential mode, as well as in multiple editors.

Lens Data Editor

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 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 in the following images.



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 16 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-Diamter 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 0.424 mm of flat surface in order to extend the lens past the Chip Zone. 



Once a circular aperature 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:



Ray Tracing Properties

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.


ISO Manufacturing Drawing

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.



Conversion to Non-Sequential Mode

Standard surfaces can be converted into non-sequential Standard Lens objects: the Clear 1 and Clear 2 parameter are the values of Clear Semi-Diameter plus Chip Zone of the front and rear surface. Edge 1 and Edge 2 are set to whatever the respective Mechanical Semi-Diameter is. The flat part of the lens front and rear is part of Face 0, which is the side wall.



Conversion for Even Asphere surfaces is also supported. 


Multi-Configuration Editor

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. 



When using the Make Thermal tool (Setup>Configuration>Make Thermal), CHZN and MCSD operands are added just as the SDIA operand is, i.e. two operands (1 MCSD and 1 CHZN) for each air/glass or glass/glass boundary.


Merit Function Editor

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 allow the user to optionally consider or ignore the Chip Zone and Mechanical Semi-Diameter when computing the operand values. 




The keyword "SETSURFACEPROPERTY" incorporates the previously discussed surface parameters as Code 27 (CHZN) and Code 28 (MCSD). The numerical functions CHZN(n) and MCSD(n) report the respective parameter value of surface n. The optimization operand functions OCOD and OPEV are compatible with CHZN and MCSD.


Parameter properties for the surface parameters may be found in the ILDERow interface, so you have direct access to the parameter value as well as the cell itself. The ILDEApertureData interface includes the Boolean DisableSemiDiameterMarginsForThisSurface, so the global Semi-Diameter Margins can be turned off/on.



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.


Availability of Parameters

These parameters are available in the Professional and Premium editions of OpticStudio only. When opened in Standard in the edition, the Chip Zone and Mechanical Semi-Diameter parameter columns in the LDE are greyed out:



If a lens file is opened that uses the new MF operands, an error message is displayed and the operands are removed from the MFE.




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