A camera (30) uses an electro-active device (11) to position a movable lens. The electro-active device (11) comprises an electro-active structure in the form of a continuous electro-active member (12) curving in a helix around a minor axis (13) which is in itself curved for example in a helix around a major axis (14). The continuous member (12) has a bender construction of a plurality of layers (21 and 22) including at least one layer of electro-active material so that it bends, on activation, around the minor axis (13). Concomitantly with the bending, the electro-active structure twists around the minor axis. Concomitantly with that twisting, relative displacement of the ends (16) of the device (11) occurs due to the combination of the twisting around the minor axis (13) and the fact that the minor axis (13) is curved. This structure of the electro-active device (11) is compact and provides for linear displacement, thereby making it suitable for positioning the lens of the camera (30).