Learning Forum

[jthujian]

The formula for calculating RMS in the Zemax manual is as follows：

In Wavefront Map, when "Remove Tilt " is chosen,  using the data shown in the txt and the formula above，I calculated the RMS by Matlab.

 Why is the RMS I calculated different from what Zemax displays？The difference between two RMS is 0.003 wave.

Why is the calculated RMS different from what Zemax displays, even if all data and RMS formulas are provided by Zemax？

[Flurin Herren]

Hi jthu-jian,

Thanks for positing here in the forum!

I think you calculation is correct; However, the is one specific caveat which you will need to consider. When OpticStudio is calculation the RMS Wavefront error it ignores pixels where there is no data. They are reported as zeros in the raw data output, but not used for the internal OpticStudio RMS calculations. Have you used the raw data output for your Matlab calculation?

 

You can always create a mask to filter out the zeros from the raw data. I have taken the Single Lens Example from the sample files (Field 2):

If you take that into account, do your calculations match up?

Best,

 

 

[jthujian]

Hi Flurin Herren,

Thank you for your reply！

1、In my calcucation, zero data in the boundary is ignored, however, the zero data in the center is keeped.

2、I completely agree with your method， when "Remove tilt" is not selected, and the RMS calculated by your method is the same as Zemax.

However,  when "Remove Tilt" is selected, the RMS calculated by your method is different from the RMS shown by Zemax. How to explain this phenomenon？

 

3、To explain this problem better， we choose the "Cooke 40 degree field.zmx" in Zemax Samples(.\Zemax\Samples\Sequential\Objectives\Cooke 40 degree field.zmx).

The setup in Wavefront Map is shown as follow. When "Remove Tilt" is not selected, the RMS shown by Zemax is 0.4909, which is same as the result calculated myself(0.490939135936001)

However, when "Remove Tilt" is selected, the RMS shown by Zemax is 0.4022, which is different from the result myself(0.399791317298713)