I guess the main confusion of defining this lens is probably the setting of depth/frequency. [bG>qe1}&
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The main fresnel lens types are: Nr9[Vz?$P
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* Constant groove depth. S I7B6c
* Contant groove pitch types. \ `&pk-uW
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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. +^? -}v
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Hope this helps!!
