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Question about accuracy of CENX/CENY

  • June 15, 2026
  • 2 replies
  • 42 views

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Dear all, 

In the manual, it is written : “Samp: The grid size. A value of 10 would yield a 10 x 10 grid of rays”. 

I need to use CENX(Y) with the highest accuracy. 

What is the maximum acceptable value of samp ? 

Is there another way to increase the accuracy of CENX(Y) ? 

Many thanks. 

Best regards, 

Thierry. 

2 replies

Mike.Jones
En-Lightened
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  • En-Lightened
  • June 15, 2026

This depends on how many waves of OPD are present at the FOV points.  If only a few waves, it's better for your extreme precision need to use the Huygens diffraction centroid.  CENX and CENY are geometric only and do not account for diffraction.  If the OPD is tens of waves then CENX and CENY are sufficient.  I start out with the default sampling values, note the centroid values, then increase the sampling until the centroid values differ only in the 4th or 5th decimal.  


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Hi Mike, 

I’m working on the design of the future space telescope HWO, and especially the distortion over hundreds field points, for which the telescope is diffraction limited. 
I know well CEHX(Y), but these operands are much too slow (even with my i9/20 cores) if you increase the accuracy (pupil and image samp). 
This is why I prefer to use CENX(Y). So, (question for the Zemax Staff) is there a maximum value for the samp parameter ? 

Regards, 

Thierry.