Surface irregularity: RMS vs no. fringes

  • 9 July 2020
  • 2 replies

Userlevel 2

Hi all,


In the tolerance wizard the surface irregularity is given by no. of fringes.

Some vendors of lens give the surface irregularity in unit of RMS Angstrom.

Is there any conversion factor between these two units?

If not, is there any other way to overcome this disparnecy?


Thanks a lot,



Best answer by Berta.Bernad 9 July 2020, 13:25

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2 replies

Userlevel 4
Badge +2

Hi Nadav,

you can use TEZI to tolerance on surface irregularity. With this operand the max tolerance value is the exact RMS error of the surface in lens units, so you can convert from Angstrom to the lens units defined in your sytem. 

You can find an example of how to use this operand in this forum thread, as well as in this article.

I hope this helps! :)


Userlevel 2

Hi Berta, 

Thanks for the answer the ref!

Best regards,