Hello, I just received my s15 kit and sadly i cannot tell the difference between the two fresnels, there is no special markings or anything. I searched the forums and nobody else seems to have this problem. would i just have to find out by trial and error after building my projector? or is there a way to get it right the first time? Thanks

I can't find the link but if you take it outside and hold it up to the sun over the say grass or table. Move it up or down until the light focuses to s sharp point and then measure the distance from the table to the fresnel. One should measure 317mm approx and the other 220mm. It's easy to tell which is which if you hold them at the same time and see which one has to be closer to the table to focus. Hope that helps and makes sense

http://www.lumenlab.com/forums/index.php?showtopic=1561