A method of focus and a focusing apparatus and a detecting module are provided. The system includes a searcher, a tracker and an assigning management unit. The first junction type compound lens comprises a first lens L1, a second lens L2 and a third lens L3 arranged in this sequence from the object side to the image side, and the second junction type compound lens comprises a fourth lens L4, a fifth lens L5 and a sixth lens L6 in this sequence from the object side to the image side.