1. Head up display (HUD) for displaying a combined image of, a scene image of a scene and an informative image, for an observer, the HUD comprising: an image source for producing a substantially small narrow angle informative image; an optical relay for producing a substantially large narrow angle informative image, by enlarging said substantially small narrow angle informative image, received from said image source; a low physical height horizontally expanding optical assembly for producing a horizontally expanded image, by horizontally expanding said substantially large narrow angle informative image, received from said optical relay; and a planar optical module for producing a substantially large informative image, by vertically expanding said horizontally expanded image, and further producing said combined image, by combining said substantially large informative image with said scene image.