The invention relates to an optical device (100) with variable aperture, comprising: - a deformable membrane (1) comprising a central optical area (1a), - a support (10, 12) to which a peripheral anchoring area (1c) of said membrane (1) is connected, - a first cavity filled with a constant volume of a first transparent fluid (2) in a determined range of wavelengths, said cavity being delimited atleast in part by a first face of said membrane (1) and a wall of the support (10), - at least one actuation device (5) of a region (1b) of the membrane located between the peripheral anchoring area (1c) and the central optical area (1a) of the membrane, configured to bend said region (1b) of the membrane by application of electrical actuation voltage so as to displace some of the volume of the first fluid (2) towards the centre or towards the periphery of the first cavity, said displacement of fluid being intended to deform the central area (1a) of the membrane, said optical device (100) beingcharacterized in that it also comprises a constant volume of opaque liquid (3) in said determined range of wavelengths, in contact at least locally with a second face of the membrane (1) opposite thefirst face and with a second transparent fluid (4) in said determined range of wavelengths and non-miscible with said opaque liquid (3).