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spheric surface tilt and decenter tolerance

  • 19 December 2021
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Hi Zemax engineer,

    I’m studying the KA-01675 about tolerance analysis.  I’m confused about the following explanaiton.

   It’s difficult to understand the word “degenerate”. 

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Best answer by Mark.Nicholson 20 December 2021, 18:54

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‘Degenerate’ in this context means ‘indistinguishable’. I hate the use of this word in scientific contexts, as it’s never used in non-scientific contexts to mean this. You’ll find it in Degenerate Four-Wave Mixing, for example.

Hope I didn’t write that KB article :joy:

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Hi Mark,

    Does it mean either “tilt”or “decenter”is sufficient for the surface tolerances?

 

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Yes. The bottom line is, for a spherical surface, use either tilt or decenters, but not both.

For a parabola, there is a single axis of rotation that you can separately decenter and tilt, and that’s generally true for rotationally-symmetric aspheres. But you can draw an many axes as you like through a sphere: there’s no single axis of rotation. Hence tilts and decenters are degenerate, indistinguishable, for a sphere.

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