Question How is a circle of light turned into a square of light using a mask with a cross. This isn't actually my homework but a challenge question. Solution I really have no idea I've looked around on the net and looked in the library but I can't find anything relevant. I don't actually understand how the cross manipulates the light to produce a square. I must ask is it even possible using light or do the same limitations experienced when trying to do this geometrically arise?