New off-axis tools for reflective system design

  • 15 October 2021
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We have recently added some capabilities that should help designers of reflective systems. In case you missed them, they are: an off-axis coordinate system for surface analyses, a sequential Off-Axis Conic Freeform, a nonsequential Off-Axis Mirror, and a tool to add an off-axis pivot point.

Off-Axis Coordinates flag

The Surface Sag, Curvature, and Slope plots now have an “Off-Axis Coordinates” flag in the Settings.  For Standard surfaces with off-axis apertures, this will convert the analyses to a coordinate system centered at the off-axis aperture and perpendicular to the surface normal at the vertex of the off-axis part.

 

 

Off-Axis Conic Freeform

There’s a new Off-Axis Conic Freeform surface with a coordinate system at the vertex of the part.  Since the freeform terms are optional, this part is also useful for mirrors that are off-axis conics.  The sides of the part are parallel to the surface normal to correctly capture parts that are fabricated directly onto a blank (rather than parts that are cut from a parent).  We have also added an equivalent non-sequential Off-Axis Mirror object.

 

 

Off-axis pivot point

We’ve added an off-axis point to our Tilt/Decenter Elements tool.  This makes it easy to tilt about the vertex of a mirror with an off-axis aperture defined.  (It’s also handy for adding mechanically realistic pivot points for a tolerancing run.)

 

 


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Thanks for this brief overview, Erin!

These should be very useful additions to SEQ surfaces and NSC objects. The specification of the mirror in “vertex coordinates” should especially help reduce “coordinate confusion.”

I also see that since you wrote this post, in release 21.3.1 (see Release Notes), there have been a couple of bug fixes.

Meanwhile, I took a closer look at the SEQ Off-Axis Conic Freeform surface and the NSC Off-axis Mirror object to see what the variable parameters are…

and I noticed that only a single Radius and Conic Constant are allowed in each.

*** How hard would it be to incorporate a Biconic type of feature (2 different Radii in X and Y, and 2 different corresponding Conic Constants)?

Colleagues and I are currently working with off-axis biconic mirror designs that might benefit from this capability.  We’re stuck with the old Biconic surfaces and objects for now and just living with (figuring out for ourselves) coordinate confusion.

-- Greg

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Hi Greg. Adding biconics isn’t on our near-term roadmap, but we’ll keep it in mind. 

The SEQ Off-Axis Conic Freeform has freeform terms on top of the conic surface, added at the center of the off-axis aperture.  So, depending on the exact shape of your biconics, you may be able to represent them using the freeform polynomial terms.

((I’d have to go to Mathematica to re-map the conic shape into the polynomial freeform terms.  Adding a parabolic profile in the X direction using the x^2 term is the simplest case.  For traditional off-axis conics such as telescope designs, with planar symmetry, the surfaces would have a spherical profile in the X direction.  So you’d want to tie the coefficients of the x^2 term and the y^2 terms using a pickup, so that the result was always a sphere.)

I believe we’re adding the freeform terms to the NSQ Off-Axis Mirror object very soon, too, as well as support for user-defined apertures.

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We have recently added some capabilities that should help designers of reflective systems. In case you missed them, they are: an off-axis coordinate system for surface analyses, a sequential Off-Axis Conic Freeform, a nonsequential Off-Axis Mirror, and a tool to add an off-axis pivot point.

Off-Axis Coordinates flag

The Surface Sag, Curvature, and Slope plots now have an “Off-Axis Coordinates” flag in the Settings.  For Standard surfaces with off-axis apertures, this will convert the analyses to a coordinate system centered at the off-axis aperture and perpendicular to the surface normal at the vertex of the off-axis part.

 

 

Off-Axis Conic Freeform

There’s a new Off-Axis Conic Freeform surface with a coordinate system at the vertex of the part.  Since the freeform terms are optional, this part is also useful for mirrors that are off-axis conics.  The sides of the part are parallel to the surface normal to correctly capture parts that are fabricated directly onto a blank (rather than parts that are cut from a parent).  We have also added an equivalent non-sequential Off-Axis Mirror object.

 

 

Off-axis pivot point

We’ve added an off-axis point to our Tilt/Decenter Elements tool.  This makes it easy to tilt about the vertex of a mirror with an off-axis aperture defined.  (It’s also handy for adding mechanically realistic pivot points for a tolerancing run.)

 

 

Hi Erin.Elliott

Thank you for the information you provided above, I want to ask if there is an option for

 

  •  “Off-Axis Conic Freeform surface” in Zemax 19.4 version?
  • “Off Conic” surface type in Zemax 19.4 version?

I searched for these two surface types in the version but could’t see

 

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