How to optimize correctly?

  • 3 January 2022
  • 1 reply

I'm practicing optimization using a few operands.
The lens performance deteriorates significantly after optimization than before optimization.
I will attach the zemax file and PPT file.

Please understand that this is an old zemax version.


How can I make the optimization process go well?

I don't know what my fault is.
Please help.




Best answer by Alissa Wilczynski 6 January 2022, 00:45

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I opened up your file and ran an optimization. I can confirm that your RMS spot radius gets significantly worse after optimizing. If you look at your merit function editor in the column “% Contribution” what you’ll see is that 99.9% of your merit function value is coming from one operand:

MNCA is limiting the merit function’s ability to find the best RMS spot size

MNCA is the minimum center thickness of air between two surfaces. You’ve set a minimum value of 0.1mm, and the current value is -0.094, meaning that there is a surface with a negative thickness. Let’s find which one…

Negative thickness on STOP to next surface

This thickness isn’t even a variable, it’s one that you’ve set. So let’s first undo the optimization to get back to your starting point, update the surface range for MNCA from 1-11 to 2-11, and re-optimize. I optimized for only 45 seconds and then stopped it, to see if we’re heading in the right direction. I can now see that the spot size has in fact reduced as expected, and that the boundary operands are not contribution to the MF value at all.