Abstract: An image projection display system comprises a variable optical property element (1). The element (1) is under direction of a control system (2) and is positioned within an optical system (5), comprising optical elements (5(a, b, c, d, e, f, g)). A source image electronic device (4) receives inputs from a video generation system (7) and is illuminated with light from a photon source (11) filtered by a wavelength-selecting colour wheel (5(b)), under direction of an illumination control system (6). The element 1 comprises a thin Al-coated membrane (150) etched from Sa3N4 (151) mounted via spacers (153) over a substrate (152) having actuator pads (154). Circuits (155) supply various control voltages Electrostatic attraction causes the membrane (150) to deform towards the actuator pads (154) when voltages V1, V2, . . . VN are applied to the actuation channels.