EFNO gives different result to that calclated in relative illumination analysis

  • 23 August 2021
  • 2 replies


I have a system with a non-circular aperture and therefore try to calculate its effective f number using the operand EFNO(effective f number). However, I get different results when using the operand EFNO, in comparison to the result given in the relative illumination analysis, despite the same setting is applied on both calculation.


(wavelength 3 is 0.555µm, and field 1 corresponds to 0 y field)






As can be seen above, one gives a value of 4.13(EFNO), while the other gives a value of 3.85. I think the latter one should be correct, but the question is why does one get different results here, do these two use different algorithms for calculation? How can I calculate this value in a Zemax macro conveniently if the result provided by EFNO is not trustworthy….



Thanks a lot in advance!



Best answer by Nicolò.Bassoli 1 December 2021, 14:45

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somehow the images are not showing up correctly… these are what I was referring to in the quesiton.



I don’t know if it’s too late, but I noticed that based on the selected sampling in the EFNO operand, the results can vary greatly. 

For example:


While the relative illumination plot give as EFNO a value of 1.604542.

The sampling of relative illumination is about 20