is positioned such its first principal focus lies at the surface of pencil focus formed by the imaging sub system 21 b when the variable power optical system 22 is in a state of maximum power this causes pencils exiting the final optical system 23 to have near planar wavefronts and so corresponding image pixels are perceived by the user to be at near infinite distances when the variable power optical system 22 is in a state of minimum power the surface of pencil focus formed by the imaging sub system 21 b lies after the first principal focus of final optical system 23 this causes pencils exiting the final optical system 23 to have near spherical wavefronts of high curvature and so corresponding image pixels are perceived by the user to be at small distances the control system 8 has inputs of pixel co ordinates and intensities from the image synthesis system 5 and required perceived distance from the scene synthesis system 4 it generates an output to the video generation system 6 of pixels to display simultaneously an output to the variable aperture limiting stop 24 of the position and diameter of pencils to form and an output to control the variable power optical system 22 to modulate pencil wavefront curvature using look direction and accommodative state inputs from an eye.