I have an asphere lens setup in NSC, and want to see the effect of adding an astigmatism to the lens. The only way I see is to use the biconic Zernike surface with all Zernike coefficients set to 0. When enter the lens prescription into the aspheric surface or Zernike surface, I get the correct results. As soon as I switch to the biconic Zernike the results look incorrect. Any ideas on why they do not match?