Hi, I'm using an aspheric lens with a LED light source for a DIY projector. As I understand it, if I place the led light source at the focal length of the aspheric lens, the light should be collimated(parallel) coming out the other side. As I decrease the distance between the led and the lens, the light coming out should have an increasingly wide beam angle, correct? Since most LED sources have a rough beam angle of 120 degrees, I want to place the lens as close as possible, but I need to make sure that the beam angle projects the light uniformly onto the fresnel lens, and take into account also the fresnel lens fl as well. Does anyone know what formula I can use to calculate beam angle, given the light source distance from the lens? It seems that the focal length and the led distance should be enough to calculate this? Thanks in advance for any help!