Abstract: An optical arrangement for a helmet-mounted display for providing binocular presentation to a pilot from a single display source or for superimposing the images from two display sources on his helmet-mounted display. In one embodiment a single display source 1 provides an image which is alternately directed between left and right eyes of the pilot by means of one scanning mirror 4 and two fixed mirrors 5a and 5b. An iris 3 opens and closes in synchronism with the movement of the scanning mirror 4 in order to prevent image distortion. Because only one display source is required, the weight of the arrangement is kept to a minimum. In another embodiment, using similar core elements the images from two display sources are alternately projected on to the pilot's visor by means of similar fixed mirrors 5a and 5b and a scanning mirror 4, but using two iris' 3+ and 3" synchronised to the mirror movements one in each optical path from display source 1' (or 1") to fixed mirror 5a (or 5b).