The conditions of the focus of thin compound lens located at different side of compound lens

The focal length and the focal position are the two principle properties of a compound lens.However,as for the conditions that the distance between the two lens and the focus of each lens in the compound lens,present references and experimental (guidebooks) instructions haven't discussed.By discussing several kinds of compound lens that contain two thin lenses,we conclude a proper condition in which the focal points of the compound lens lie at the different side of the compound lens respectively,and give us some theoretical guidance for the combination of lenses in optical experiment.