Tunable compact optics are the next step to nature-inspired soft robotics. Yet, current technologies often require rigid components that cannot compete with the superior adaptability of soft matter. Here, I present a soft lens that achieves large focal length changes at moderate voltages and easily resists small deformations. A zipping electroactive polymer actuator displaces liquid to inflate a membrane with 6mm diameter and thus reduces the focal length within milliseconds. A mixed numerical-analytical model of the soft lens provides accurate predictions of lens performance and helps to optimize design parameters. As a result, a focal length change from 550 to 22mm is achieved with less than 500V applied voltage. Response times of approximately 250ms resemble near accommodation of the young human eye. The lens presented here is not only a new type of soft optics, the model and its findings also make a significant contribution to future low voltage electroactive zipping polymer systems.