Rainbow hologram

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The rainbow hologram or Benton hologram was invented in 1968 by Dr. Stephen A. Benton at Polaroid Corporation (later MIT). Rainbow holograms are designed to be viewed under white light illumination, rather than the more esoteric laser light required previously. The rainbow holography recording process uses a horizontal slit to eliminate vertical parallax in the output image, greatly reducing spectral blur while preserving three-dimensionality for most observers. A viewer moving up or down in front of a rainbow hologram sees changing spectral colors rather than different vertical perspectives. Stereopsis and horizontal motion parallax, two relatively powerful cues to depth, are preserved.

This invention illustrates an underlying theme of Benton's work: to reduce the amount of information in a hologram to more closely match the requirements of the human visual system.

The holograms found on credit cards are examples of rainbow holograms. These very common holograms are technically transmission holograms mounted onto a reflective surface like a metalized polyethylene terephthalate substrate commonly known as PET in the holographic industry. The Rainbow Holographic process can also be applied to very large sheets of holographic film, resulting in what is known as a large format Rainbow Transmission Hologram.

[edit] Large Format Rainbow Transmission Holograms

Large Format Rainbow Transmission Holograms are made using the system described above, with a horizontal slit master hologram recorded that captures only the horizontal information of the three dimensional model. These type of holograms can be made with either continuous wave or pulse lasers. If using a continuous wave laser, and exposing very large pieces of film (up to 2 metres x 1.1 metre) stability of both the 3D model and the film becomes a critical and difficult issue. However the results can be spectacular with image depths of 5-6 metres possible and the (in focus) protrusion of the holographic image up to 600mm in front of the holographic film plane, possible.