I guess the main confusion of defining this lens is probably the setting of depth/frequency. @f-X/q]P
Y<xqws
The main fresnel lens types are: zeHF-_{
!%G]~
* Constant groove depth. DXiA4ihr=
* Contant groove pitch types. 6{y7e L3!
Cs6`lX >
So if your depth is fixed you will define +ve value in the cell and to specify the "height" or "depth" of each groove feature. If the frequency of the groove is fixed then you use -ve value. Say putting down - 5 this implies that there are 5 grooves with a unit length. %#x4wi
86r"hy~
Hope this helps!!