Why is surface Clear Semi-Diameter not Opening fully for all rays to pass through?

  • 14 June 2024
  • 2 replies

Hi all gurus,

I have a sequential model of a lens here with a lens and a flat PMMA sheet. Some of my rays from higher field angle (colored green) pass through outside of the (auto set) clear semi-diameter.

Is there a setting in my model that I overlooked here?


Please advise and thank you very much.




Kin Hing



Best answer by Mike.Jones 15 June 2024, 02:07

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Userlevel 7
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Not an answer, but it seems to be an edge case. If you change the Radius of Surface 2 from -4.671973 to -4.75, you get the following 3D Layout:

We see that the upper marginal ray of the most extreme field (blue in my 3D Layout), is really at the edge of Surface 2, I wonder if its causing the issue. Even with a Radius of -4.671973, the single raytrace of this marginal ray seems to be normal though.

With the Merit Function, I guess you could figure out what should be the size of this aperture, and perhaps even calculate it automatically as a solve, but that’s probably not what you want to do anyways.

I hope this helps troubleshooting the problem and take care,



Userlevel 5
Badge +3

Automatic semi-diameter calculations often overlook aberrations around aperture edges.  Setting aperture sizes as apertures and updating ray aiming will usually (but not always) fix the problem.  If you absolutely have to have zero vignetting, you have to “play” with aperture sizes using layout plots until all the rays are transmitted.  Even after that it’s still good to update ray aiming.  This is a long-standing Zemax problem.