Tolerancing Overview

OpticStudio provides a flexible and powerful tolerance development and sensitivity analysis capability. The tolerances available for analysis include variations in construction parameters such as curvature, thickness, position, index of refraction, Abbe number, aspheric constants, and much more. OpticStudio also supports analysis of decentration of surfaces and lens groups, tilts of surfaces or lens groups about any arbitrary point, irregularity of surface shape, and variations in the values of any of the parameter or extra data. Since the parameter and extra data terms may describe aspheric coefficients, gradient index coefficients, and more, any of these values may also be made part of the tolerance analysis. The various tolerances may be used in any combination to estimate alignment and fabrication error effects on system performance.

OpticStudio always uses exact ray tracing for tolerance analysis; there are no approximations or extrapolations of first order results in the OpticStudio tolerance algorithms.

Tolerances are defined using operands, such as TRAD, which defines a tolerance on a radius. The tolerance operands are automatically saved with the lens file. Tolerance operands are edited on the Tolerance Data Editor, available from the Editors group of the "Setup Tab" or in the "Tolerance Tab".

Tolerances may be evaluated by several different criterion, including RMS spot radius, RMS wavefront error, MTF response, boresight error, user defined merit function, or a script which defines a complex alignment and evaluation procedure. Additionally, compensators may be defined to model allowable adjustments made to the lens after fabrication. OpticStudio also allows limits to be placed on the change of a compensator.

Tolerances may be computed and analyzed three ways:

Sensitivity Analysis:

For a given set of tolerances, the change in the criterion is determined for each tolerance individually. Optionally, the criterion for each field and configuration individually may be computed.

Inverse Sensitivity:

For a given permissible change in criterion, the limit for each tolerance is individually computed. Inverse sensitivity may be computed by placing a limit on the change in the criterion from nominal, or by a limit on the criterion directly. The criterion may be computed as an average over all fields and configurations, or on each field in each configuration individually.

Monte Carlo Analysis

The sensitivity and inverse sensitivity analysis considers the effects on system performance for each tolerance individually. The aggregate performance is estimated by a root-sum-square calculation. As an alternative way of estimating aggregate effects of all tolerances, a Monte Carlo simulation is provided. This simulation generates a series of random lenses which meets the specified tolerances, then evaluates the criterion. No approximations are made other than the range and magnitude of defects considered. By considering all applicable tolerances simultaneously and exactly, highly accurate simulation of expected performance is possible. The Monte Carlo simulation can generate any number of designs, using normal, uniform, parabolic, or user defined statistics.

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