The invention relates to holographic head-up displays, to holographic optical sights, and also to 3D holographic image displays. We describe a holographic head-up display and a holographic optical sight, for displaying, in an eye box of the display/sight, a virtual image comprising one or more substantially two-dimensional images, the head-up display comprising: a laser light source; a spatial light modulator (SLM) to display a hologram of the two-dimensional images; illumination optics in an optical path between said laser light source and said SLM to illuminate said SLM; and imaging optics to image a plane of said SLM comprising said hologram into an SLM image plane in said eye box such that the lens of the eye of an observer of said head-up display performs a space-frequency transform of said hologram on said SLM to generate an image within said observer's eye corresponding to the two-dimensional images.