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Zernike Standard Sag -

  • September 4, 2024
  • 2 replies
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Olieli

Hi,

 

I just had a micro-optic measured (outsourced) to obtain it’s true form.

I got back a RoC, and 36 Zernike coefficients (Standard, Fringe and Annular).

I’m trying to plug into Zemax - but I’m having a hard time understanding several things:

  1. Zemax still gives the Even Asphere terms - are they not described by the Zernikes?
    1. Would I need those terms measured separately?
  2. What number do I put in for the Norm Radius?

Thanks,

 

Eli

Best answer by Michael.Young

Hello @Olieli,

Zernike coefficients can be tricky and when to use the different surface types is not always clear.

Let’s assume that the coefficients provided are for sag. They are likely to be Standard or Fringe. Annular is unlikely unless the optic is annular.

The manual shows the sag equation for either the Zernike Fringe Sag and Zernike Standard Sag as,

Zernike Sag Equation

The equation shows that the surface is the composite of “three” terms. The first is the curvature and conic term. The second is the aspheric summation. The last is the Zernike summation. If the report does not provide any aspheric terms then those fields can remain unpopulated in the surface description.

Hopefully, the report would provide the normalization radius; however, if it does not, I would see if there is a clear aperture specified and use its half-value (semi-aperture) as the normalization radius. If there was a sag table provided, Zemax can provide a sag table representation of any surface and that can be used as a check that the surface was entered correctly.

The coefficients for the two types are a little different and hopefully the report states what type or the coefficients which would then indicate which type.

For example, Zernike Standard Polynomials are,

Zernike Standard Polynomials

and the Fringe Polynomials are,

Zernike Fringe Polynomials

Hopefully that helps to clear things up.

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Michael.Young
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Hello @Olieli,

Zernike coefficients can be tricky and when to use the different surface types is not always clear.

Let’s assume that the coefficients provided are for sag. They are likely to be Standard or Fringe. Annular is unlikely unless the optic is annular.

The manual shows the sag equation for either the Zernike Fringe Sag and Zernike Standard Sag as,

Zernike Sag Equation

The equation shows that the surface is the composite of “three” terms. The first is the curvature and conic term. The second is the aspheric summation. The last is the Zernike summation. If the report does not provide any aspheric terms then those fields can remain unpopulated in the surface description.

Hopefully, the report would provide the normalization radius; however, if it does not, I would see if there is a clear aperture specified and use its half-value (semi-aperture) as the normalization radius. If there was a sag table provided, Zemax can provide a sag table representation of any surface and that can be used as a check that the surface was entered correctly.

The coefficients for the two types are a little different and hopefully the report states what type or the coefficients which would then indicate which type.

For example, Zernike Standard Polynomials are,

Zernike Standard Polynomials

and the Fringe Polynomials are,

Zernike Fringe Polynomials

Hopefully that helps to clear things up.


Olieli
  • Infrared
  • September 5, 2024

Thank you @Michael.Young 


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