Apparatus for displaying an image suspended in space

Apparatus for displaying an image suspended in space comprises an object (1) for display, a retroreflector (2) receiving light from the object, a beamsplitter (3) in a path for light from the object to the retroreflector, and a concave mirror (4) between the beamsplitter and the retroreflector. The beamsplitter makes an oblique angle to the direction (6) of propagation of the light such that it transmits some light. Light from the beamsplitter is reflected by the mirror to the retroreflector which reflects it back via the mirror to the beamsplitter. This retroreflected light is reflected by the beamsplitter to form a real image (5) suspended in space. The use of a concave mirror improves viewability over apparatus including a converging lens because unwanted reflections from the surfaces of the lens are eliminated.