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Question

rays intersect problem


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Hi everyone,

    I’ve been working on the microscope objective design and stumbled cross a design in Zemax design templates. Rays don’t intersect exactly on the stop surface(10th) even with the “paraxial”ray aiming on. Why is that? I expected the rays would intersect exactly on the stop surface.

    

6 replies

David.Nguyen
Luminary
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Hi @steven.Ou,

 

Is this design in the sample files? Which one is it?

Have you tried Real Ray Aiming as well? There’s also been a relatively recent release of “enhanced” ray aiming that might be useful for you:

https://support.zemax.com/hc/en-us/articles/4415991777299-Introduction-to-Enhanced-Ray-Aiming-and-Ray-Aiming-Wizard

Take care,

 


David

 


MichaelH
Ansys Staff
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  • Ansys Staff
  • 345 replies
  • July 12, 2023

Hi Steven, 

If you look at the Field Data Editor, you can see that there are Vignetting Factors for Field 2 and Field 3.  Vignetting Factors intentionally make the rays for different fields to not overlap at the Stop location.  If you remove the VDY, VCX, & VCY you will see the rays intersect at the Stop location:

@David.Nguyen The file is the first microscope after the Boge design in the Libraries > Design Templates.  This used to actually have a name in Zebase but now that it’s in Design Templates, the file is loaded as a temporary file so you can’t easily find it except going through the Design Templates.


David.Nguyen
Luminary
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Thank you @MichaelH! Can you comment on why one would want to intentionally not overlap the fields at the Stop? Thanks a lot :)


MichaelH
Ansys Staff
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  • Ansys Staff
  • 345 replies
  • July 14, 2023

Hey David,

Rather than thinking of “overlapping fields at the Stop”, remember that Vignetting Factors are a tool that should only be used early on in the design during optimization and final analysis should remove Vignetting Factors and ensure all surfaces have a hard aperture (this is what the Design Lockdown does).  A designer would use the Vignetting Factors early in the design if they know there will be a limiting aperture for off-axis fields because of size or geometry constraints.

Vignetting Factors is an approximation for early analysis to ensure that all 4 marginal rays make it through the system since a few Optimization operands rely on the marginal rays, but this approximation uses an ellipse rather than the actual Cat’s Eye you get for vignetted off-axis fields.  To get the actual analysis of a final design, the full beam footprint should be used for each field.


David.Nguyen
Luminary
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Brilliant @MichaelH, thank you!


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  • Author
  • Ultraviolet
  • 26 replies
  • July 15, 2023

HI @David.Nguyen  @MichaelH  ,thank you, guys.

 


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