Inquiry 9: How Does It Work? 3D Images and Holograms
Stereoscopic, or 3D, photography works because it is able to recreate the illusion of depth. Our eyes are about 6.5 centimeters apart, so each eye sees something different. If you view two photographs that are taken the same distance apart with a stereoscope, then you are able to perceive depth. To demonstrate how our eyes see things differently, encourage students to hold one of their fingers about a foot from their nose and close one eye. Then ask them to reopen it and close the other. They will see that their finger appears to jump from side to side.
The principles of three-dimensional, or 3D, images were known even before photography was invented. Charles Wheatstone experimented with stereoscopic drawings of simple objects in 1832. After the discovery of photography a few years later, the two principles were combined and stereoscope viewers were produced, quickly becoming a very popular form of home entertainment. In 1844 a technique for taking stereoscopic photographs was demonstrated in Germany, and David Brewster developed a much smaller and simpler viewer that used prismatic lenses in Scotland. The viewer was used to look at cards called stereographs, which were twin photographs with two images mounted side-by-side. Each picture was taken from a slightly different viewpoint equal to the spacing of the eyes. When looked at through the stereoscope viewer, the picture appeared as a three-dimensional image.
The stereoscope is generally considered a form of mass media. Before the advent of radio and TV, this instrument allowed many people to "travel" to far off lands without leaving home. Some things that particularly interested people were the pyramids and tombs of ancient Egypt, the sights of New York, Chicago, and San Francisco, and the abbeys and countryside of Europe. The great events of the day also found their way into stereo slides. Among these were the building of the Panama Canal, War World I, the Johnstown Flood, and the San Francisco earthquake. The Chicago World's Fair of 1892 and the St. Louis World's Fair of 1904 could be enjoyed even by those who could not be there.
Anaglyph images are the type of 3D images with which you are probably most familiar. Louis Ducas Du Hauron, a French scientist, patented this method of stereoscopic photography in 1891. It involves a pair of images taken from slightly different points, which are color corrected and superimposed so that one image is offset slightly from the other. Typically the image for the left eye is printed in red ink and the right eye image is printed in green ink. When observed with the naked eye, the image looks overlapping, doubled and blurry. However, when viewed through a pair of glasses with different colored lenses, the image appears to be three-dimensional. The glasses used to view these objects are usually red and blue with the red lens covering the left eye and the blue, or sometimes green, lens covering the right eye.
Activity - Have students design a series of stereoscope programs that show a current or historical event. Discuss why the depiction of events was more important around the turn of the century.
The method of making 3D photographic images without a lens is called holography and the images are called holograms. A British physicist, Dennis Gabor, developed theories involved with holography in 1947. However, the first production of holograms did not take place until the 1960's when laser technology became available.
Holography has very little in common with regular photography. Holograms contain information about the size, shape, brightness, and contrast of the object being recorded. Lasers are used to produce holograms because their light is one color and highly directional. Holograms record images of light waves emitted from a laser as they are reflected off an object. The hologram, when lighted and viewed under ordinary light, presents a three-dimensional re-creation of the original object.
Today holograms are used for security purposes, commercial and consumer applications, and promotional pieces. They are, for instance, frequently used to protect financial documents, credit cards, and paper money. The reason for using holograms for such purposes is that they are very difficult to copy. Holograms also appear on greeting cards, collectibles, trading cards, packaging, and displays, as well as T-shirts, tags on merchandise, stickers, and key chains.
Activity - Place students in small groups and have them create a list of all of the places they have seen holograms. Then compile a class list after each group has completed their group list. Ask students to comment on the reasons why these are used. Also, explain to them that some people believe that, in the very near future, holograms will be broadcast over television. Encourage students to discuss and write about how television in general, or their favorite TV program, would change if this happened.
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