I guess the main confusion of defining this lens is probably the setting of depth/frequency. fG.w;Aemv5 m4%m0"Z The main fresnel lens types are: D_8hn3FH ) ejvT- * Constant groove depth. 0~-+5V * Contant groove pitch types. D@3|nS X!"y>J 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. 8m9G^s`[ P"~B2__* Hope this helps!!