Adjusting the focal length of a camera lens allows you to change your angle of view. Miniature lenses can achieve this change by using a method called electrowetting. Electrowetting involves changing the balance of forces at a contact point of a free surface and a solid by applying a voltage. However, focus is not obtained immediately due to oscillations in the free surface. Here, we investigate the optimal viscosity for critically damping the free surface when a voltage is applied.