Real-time accurate positioning of laser beams and optical images on 3D targets, as well as focus correction in the flat field laser scanning, are provided by dynamic focus systems. Commonly used zooming devices involve rather complex driving mechanisms to control the relative motion of the lens systems. A possible, cost-effective alternative to this approach is to use a lens with variable focal length. The design of a dynamic focus system based on this principle is presented, and a suitable driving method, using electrostatic interactions, is also proposed. Dimensional design formulae are given, together with performance evaluation calculations.