Sag maps in off-axis coordinates

  • 21 June 2024
  • 8 replies
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E
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In case you missed it, our sag maps now have an automatic setting that will automatically report sag in off-axis coordinates.  This is helpful for users who regularly work with off-axis mirror and freeforms. (We’ve added this option to our slope and curvature maps, as well.) 

The sag is reported in a new coordinate system centered on the off-axis vertex and with tilt across the aperture removed.  Tilt values are reported out in the graphic.  Exact sag data can be retrieved using the SSAG operand, where the “off-axis” option is also available.  Tilts and other information about the data can be retrieved using the DSAG operand.

 

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Erin

8 replies

Sean Turner
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Hi Erin,

I have been working with a lot of off-axis mirrors lately, and this post made me take a look at this feature again. Tilt values are not calculated when a User Aperture is applied, which is not mentioned in the help file. From the help file for Surface Sag, it looks like User Aperture would work as well as any other valid aperture.

Off-Axis Coordinates When checked, the plot will consider any apertures defined in the Surface Properties of the surface. The coordinate system for the sag computation will have an origin at the vertex of the off-axis part.

Valid apertures for this option will be: Circular Aperture, Rectangular Aperture, Elliptical Aperture, User Aperture, and Floating Aperture.

This option does not support surfaces that have tilt terms at the vertex of the surface, such as Tilted surface types.

The sag is plotted, but only shifted by any X and Y decenter. The shape of the aperture is shown, but the tilts are not calculated. We use a racetrack shaped aperture on many of our mirrors, and when I changed one to a rectangular aperture of the same X and Y half-width, the tilts were then reported in the analysis window.

This leads me to mention again this feature request.

Regards,

Sean

Sean Turner
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One more thing. It would be great if you could add global coordinate data for the center of the off-axis aperture. It takes me close to 20 merit function operands to get the global Y and Z coordinate for an off-axis segment on an even asphere with decentered aperture. Is there an easier method? 

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Hi, Sean. 

  • Could you send your UDA case in to support@Zemax.com?  I just double-checked a UDA aperture and it correctly found both tilts and decenters, so maybe the obscuration in yours is causing trouble.  I wouldn’t expect this to work correctly if you put the decenters *in* the UDA data; those need to be present in the “Decenter” fields of the Aperture.
  • The rectangular aperture with rounded corners would require users to give a radius of the rounded corners, I think.  Programmatically, that would be a bit difficult, so the UDA is the best workaround at this time.
  • Do you have a gut ray in your system, that strikes the surface at the aperture center?  You can get the global coordinates and angles of where it hits the surface using RAGX|Y|Z and RAGA|B|C.  That’s what I usually do.  
Erin
Sean Turner
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Hi Erin,

Thanks for the reply. I just downloaded your OAP example file, changed the aperture on the OAP surface from Circular to User Aperture. I edited square.uda to have 30mm half-width and tilts are not calculated in the Surface Sag analysis window. I can send this to support@zemax.com as well.

 

I do not always have a gut ray at the center of the off-axis segment, so calculating the global coordinates has to be done manually. It would be nice to have this information available whenever a decentered aperture is used. 

Sean

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Hi, Sean.  I’m not able to reproduce your bug.  Are you using our latest release?  24R1.03?

Agreed - I like the idea of operands that directly return the aperture vertex.  There are workarounds, but they are cumbersome.  In the meantime, maybe a field angle optimized to hit the correct XY location on the surface, but then set it to “Ignore” in the FDE when it’s not needed.

Erin
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Oh!  You might also want to check out the Off-Axis Conic Freeform.  It has an origin at the vertex in a native way, and allows polynomial additions on top of the off-axis conic shape.  You may be able to pretty easily convert your current surfaces into this polynomial form, using analytic term matching, or just by optimizing on the freeform polynomial terms.

Erin
Sean Turner
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I am using Ansys OpticStudio 2024 R1.03.

I’ve played a little bit with the Off-Axis Conic Freeform, but have not put in the effort to convert this system to the new surface. Perhaps I’ll give it a try the next time I start a new design. 

Sean Turner
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Same file with a rectangular aperture. Surface Sag window 1 is the same, but now tilt is removed from window 2.

 

I realize the square.uda file I referenced above may not be an example included with the software. This is the format of my UDA file.

-30 -30
-30 30
30 30
30 -30
BRK

I also tried it with LIN preceding the first 4 lines. It still did not show any tilt in window 2. 

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