This paper develops a methodology for a design of zoom-systems, which are composed of thin optical components with a variable focal length (e.g., membrane lenses). The proposed procedure allows us to design not only the outer parameters of the system (focal lengths and separation of lenses), but the inner structure of individual components of the system can be calculated as well (radii of curvature, thicknesses, and refractive indices) i.e., the starting values of the mentioned parameters can be calculated and used for the next optimization.