WWe report a modeling framework for evaluating the performance of piezoelectrically actuated MEMS tunable lenses. It models the static opto-electromechanical coupling for symmetric configurations of piezoelectric actuators based on the laminated-plate theory, linear piezoelectricity, and ray tracing. With these assumptions, it helps to find geometrical parameters for actuators on clamped square or circular diaphragms that give a diffraction-limited tunable lens with minimum F-number. The tunable lens' optical performance and its focusing capability, alone and in combination with a paraxial fixed lens, were calculated in terms of object distance and actuation voltage. Using the modeling framework, we confirmed that the modulation transfer function for objects located at different distances remains the same after voltage adjustment.