A friend of mine asked if there was an easy way to output the principle planes of a system in Zemax? I am sure I have done it before, but I figured it would be best to ask the experts. Therefore, @Isaac or @hkang do you guys have a suggested method?
There is most certainly a way to export this data! Under the Analyze tab, within the Reports section (look close to the right hand side in the default ribbon) there is a tool to output the Cardinal Point Data.
For a more in depth report, the Prescription Data report contains a lot too!
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Also, in the Merit function editor, you can use CARD operand to get cardinal points.
Btw, those points were not accurate if the system is off-axis or using freeform.So the user should always double-check.
That’s a really good point! When dealing with freeform system, our notion of Gaussian optics behavior starts to break down. However, as a more optical philosophy question, when does the Gaussian approximation really not apply?
Even a spherical surface doesn’t follow Gaussian behavior perfectly because of aberrations. For example, lets say I have a spherical surface and then I add 2 waves of astigmatism to the surface. Does this freeform surface no longer have well defined cardinal points? I would argue that it does, which begs the question, when does it not? 10 waves? 100?
I think the boundaries of when and how to apply the first order optical principles to a freeform system are not very clear, and the tools to evaluate our assumptions should be developed further. What techniques have you used @hkang to evaluate when you can use first order optics in a freeform system?
As mentioned above, the principal plane poss are given in the prescription output. Also, there is a Knowledge Base article showing how to display them on the layout plots.
Principal planes suffer from the same restrictions as paraxial optics, so
- angles of incidence as small enough that sin(theta) ~ theta
- We can neglect surface curvature, so the surface can be approximated by a flat plane with equivalent power to the surface vertex
- angles are small enough that we can replace angles with slopes
These approximations mean that paraxial optics are only useful as a limiting case of most optical systems, in which the aperture limits to zero. So it’s not so much that the calculations are ‘wrong’ when applied at higher angles out with freeform, as much as they simply don’t apply.
- Mark
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