The invention relates to a tunable lens where the optical power can be adjusted. The lens consists of a deformable, non-fluid lens body sandwiched between a thin, flexible membrane and transparent back window, and an actuator system serving to change the overall shape of the membrane and lens body. The membrane is pre-shaped to have a Sag or Sagittal of at least 10 μm so that the lens has a non-zero optical power when the actuator system is not activated. In order to achieve a large optical power range for the lens, the membrane should preferably be made of a material having a Young's modulus in the range 2-1.000 MPa.