Definition: Photographic image which, when suitably illuminated, reconstructs a same-size three-dimensional image of the original object as seen from the position of the film at the time of exposure. * A hologram is a recording of the interference pattern created by the interaction of two beams of coherent light which are derived from the same source: a reference beam which illuminates the recording medium and the object beam, which is that reflected from the object. The result of interference between these two beams is a diffraction grating. * This produces an image beam that reconstructs the original wave-front from the object as an image of the object -- usually with full parallax or three-dimensional information -- but only when illuminated by a replica of the reference beam e.g. white light shining on the hologram at the same angle as the reference beam shone on the film.
Patently stupid thing to do
You may remember that holograms were the 'wow' of the visual world some years ago. So why did it sink almost without trace in the art world, only to survive on bank notes and credit cards? That it was a hellishly tricky and expensive laboratory habit is only part of the story. It did not help that some of the great pioneers were also too greedy. A case in point is that one geometry for creating rainbow holograms was patented by Stephen Benton (hence also known as a Benton hologram). This restrictive move was symptomatic of a lack of openness amongst some leading early holographers which sadly led to the inevitable last quack of their Golden Goose. What would have happened to photography had Fox Talbot won his attempt to stifle the collodion process?

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