Photography in Three Dimensions

Visitors to London's Royal Academy of Arts in March 1977 saw demonstrated a new and fascinating concept of photography, a 20th-century photographic miracle called "holography." On display at the exhibition was a floating three-dimensional image of a telephone, suspended in thin air, and so realistic that you would be excused for attempting to make a call with it.

The exhibition, designed to impress the public with the science and fun of laser beams, was fittingly named "Light Fantastic." As the visitors came to realise, with holography, instead of having the picture on a flat card, an image is projected in full three-dimensional form in space. You can actually look at it from various angles to see different parts of it.

You may have heard the word "holography" or "hologram" in connection with the recent uses of laser beams for entertainment purposes. In laser beam lightshows, swirling, darting, twisting multi-coloured laser beams are choreographed to music, and sometimes the 3-D imagery of holography is used for special effects.

How It Works

The word "holography" is used to describe the process, because the prefix "holo" means "entire" or "complete." Holography takes the picture in a much more complete manner than is achieved with an ordinary camera.

We can understand the basic principle behind holography by comparing it with sound recording and reproduction. Consider, for example, a symphony orchestra playing a piece of classical music. The musical notes and tones generated by various instruments result in a complex pattern of sound emerging from the orchestra. This pattern can, of course, be recorded, the record "storing" the sound in a coded form (actually by variations in its grooves). When the record is played, a pattern of sound is produced that duplicates the original notes that came from the orchestra. The identical sound waves have been regenerated.

In a similar manner holography records light waves for later reconstruction. Let us see how this is possible.

First of all, what is involved in seeing another person, a scene or an object? As we cannot see in the dark, light is necessary from the sun or from some other source. In fact, every tiny part of an object we are looking at reflects the light, but in varying amounts and in varying colours. A complex pattern of light is thus produced, emerging from the object like the sound emerging from the orchestra. We see the object when this pattern reaches our eyes and is interpreted by the brain.

Let us suppose that the pattern of light waves emerging from a friend sitting opposite to you is interrupted and recorded, or "stored," similar to the gramophone record's "storing" the sound. Your friend gets up and leaves. On "playback" of this "light-record" the identical pattern of light could be regenerated and thus, to the eye and brain, the person would seem to reappear. Furthermore, since the regenerated light duplicates the original (as in the case of sound reproduction), the image that is seen is in full 3-D form, exactly like the person.

This is the key difference between photography and holography. Photography involves making a flat image of a scene or of a person, like an artist's painting, but holography reconstructs the original pattern of light waves themselves.