Question

How to tolerance for coma ?

  • 15 December 2023
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This question came up in a support call, as coma was clearly the worst offender in the system.
The strategy here is to use the Merit Function value and use it as the criterion for tolerancing.
The issue is that the COMA operand is calculated from the Seidel coefficients, and is not valid for non paraxial systems. The values are then not accurate for systems with tilts & decenters, and can then not be used for tilt & decenter tolerance analyses.

The solution is to use the formula used by the Full Field Aberration tool:

 

As described in the help file, the coma computation is using Zernike terms:

We can then build the Merit Function accordingly:
 

The quadratic sum operand QSUM is the only one to have a non-zero weight, the value of the Merit Function will then return the coma.
 


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