Hi Jerry, 

There are two surfaces that have a periodic term and an even aspheric (16 order). They are in the 'User Defined' surface type, and the DLL is 'US_EAPERIODIC.DLL' and 'US_ZERNIKE+MSF.DLL'. The second one is similar to the first, but also has Zernike terms.

For more information on these surfaces, please refer to the Help File under The Setup Tab > Editors Group (Setup Tab) > Lens Data Editor > Sequential Surfaces (lens data editor) > User Defined 

Finally, we have a KBA article on the latter surface, 'Constructing mid-spatial frequency tooling errors for evaluation and tolerancing'

I hope this helps.

-Kats Ikeda

Hi Kats,

Thanks for the previous reply. When I tried this method and load the zenike+msf.dll, it said cannot load dll. Other dll worked. Can you help advise? 

Hi Jerry,

It does like you will need to get a Subscription license, either premium or professional, to run this feature. Most new features coming out in the last year or so have been for Subscription licenses, though improvements to existing features continue to be made for perpetuals. Our sales team at sales@zemax.com can help you to get a conversion if you wish.

Best regards,

Kevin