Good morning everyone. I have a question for the community. I am doing an optical project in which I need, as the title says, to concentrate white light in a very small point, with a diameter of the order of microns, so that I can pass light through a pinhole. I've been trying it with some lens sets using a halogen lamp but I can not get a point small enough. How could I get this? I would greatly appreciate if you can, in addition to advising me on this issue, send me some bibliographical sources from which to consult, thank you very much.