Hi @Théo S-L,

Would you have a minimal example that demonstrates the issue to share with us? Obviously, we can see that you’ve worked on this model for a long time, and you know about it very well. But, at least for me, it is quite difficult to understand based on the information that you shared.

These are some pointers and question that I think will help you get an answer:

• How do you do the raytracing in the ZOS-API? Are you using the BatchRayTrace or the NSCRayTrace? If the latter, have you tried to use the method ResetRandomSeed() just in case?
• Have you played with the Sampling Method of your source (Sobol vs Random), and if so, what difference does it make?
• I’m not too sure if its relevant because I don’t understand how you get the shape error but do rays get lost during the tracing?

Hopefully someone will be able to help you.

Take care,

David

Hi David,

Thank you very much for taking the time to answer me.

I dont know what details I have to share to be clear enough without flooding the content.

I present below the zemax model I am using (SUT means Surface Under Test, so here a mirror). The movable head passes above the SUT taking successive acquisitions of the punctual slope (each measure is a point in the curves presented on the first post).
For example, the scan of a cylinder mirror should begin to touch the sensor at the very bottom, then move upwards. A perfect plane mirror should be read by the sensor by an immobile point in its center. For other mirrors, the distance between the center of the sensor and were the beam touches it will indicate the punctual slope. I hope this will help you a little.
The slope measurement comes from a convergent lens (or FT lens) in the receptive head which only transmit the slope on the mirror at the measured area, and an open penta-prism in the movable head.

I will be happy to share more details if needed.

Concerning your list;

•  I’m using the NSCRayTrace (zNSCTrace) with the parameter 'randomSeed’ set to 0. But thanks for you idea, I will try using ResetRandomSeed() just to be sure. Or also try BatchRayTrace.
• Its the first time I am learning about the Sampling Method, I will also go that way for my next tests !
• Only a few rays (considering how many are simulated during the process) touch on the sensor. I had to increase the Maximum Intersection per ray for my model to work.

Even if I do not find a solution, your answer gave me new insights so thank you, I will test all of that.

Have a nice evening.

Théo.

Hi Theo,

Just to be clear, do you see this problem only when using ZOS-API for the automation, or when using the UI itself?

• Mark

Hi Mark,

To plot one of the curves shown in one of the first two figures, I used ZOS-API. In order to do this, I need to take 101 points, meaning my python code calls zemax 101 times, with 101 different positions of the movable head.

Then I analyze it: I substract a 1rst oder polynomial, a reference, and I integer the curve.

To do the same using only the UI itself would require at least 10 points, and an investment of a considerable amount of time (modifying my code for a manual entry). Moreover, I'm afraid of introducing new variables (not doing exactly the same than python), and that would call into question any conclusions I might draw.

I understand that I need to identify the source of my problem and your question is legit. I'll do this study as a second step if I don't get answers with simpler/quicker tests. 

By the way, thank you very much for reminding me this approach!

Best regards,

Théo.

Hi David and Mark,

Thank you again for your help!

I solved my problem thanks to your comment about the sampling method David,
with the random method I don’t have the issue.
Moreover, I understood its source thanks to your article 'Understanding Sobol sampling’ Mark.

I just have to send 300 times more rays to maintain the desired precision, which is another problem.

Thanks again and have a good day !

Théo.