Stereography / 3D

[Introduction]
[My stereographic / 3D images]
[Stereographic / 3D images from other sources]
[Links]

Introduction

Stereography is the process of using a pair of 2D (flat, "planar") images, to create the perception of a 3D image in the mind of the viewer - the so-called "cyclopean view". The two images are of the same object or scenery, but taken from two slightly different positions (normally not different angles). Stereographs have been made since the 1840s!

The pair of 2D images normally requires a special viewer: a stereoscope. However, there are also several "free-viewing" techniques that do not require a viewer. The latter viewing technique requires practice - using a viewer is much easier. Some people have impaired vision, or have a brain that does not fuse the 2D images from the eyes into a single 3D perception. Such people suffer from stereopsis and are stereo blind.

To mimic a pair of eyes, we need a camera to take two pictures of an object. For moving objects, the pictures must be taken simultaneously. This implies either a camera with two lenses, two (identical) cameras that are mounted side-by-side, or a single-lens camera with an optical splitter-attachment. Of course, such a stereo-camera can also be used to take pictures of static objects. However, this can also be done with a single-lens camera that is moved slightly sideways between taking the pair of pictures.

The standard distance between the lenses of the stereo-camera, or between the two positions of the single-lens camera, is about 6.3 cm (2.5 inch). This distance, called the stereo base, corresponds to the distance between the pupils of the eyes of an average adult. As a general rule, a base is optimal for objects at a distance of about 30x that base. In the standard case, this is 30 x 6.3 cm = 2 meter (6½ ft). A (much) larger base is required for large scenery such as landscapes. This is called hyper-stereo. It can also be used to exaggerate the depth effect. Conversely, a (much) smaller base is used for small, nearby objects ("macro"). This is called hypo-stereo.

The picture-pair must then be presented to the viewer. The classic method is to print both pictures and mount them side-by-side (ortho-stereography) on a rectangular piece of cardboard. The result is called a stereo-card. The card is then viewed with a magnifying viewer - either a "Holmes" viewer or a "lorgnette" pair of lenses. The lenses are prismatic (wedge-shaped) to increase the perceived focal distance. Alternatively, the prints can be mounted one above the other ("view-magic" style). Obviously, the viewer has to be compatible with this. Instead of printing pictures from negative film, diapositive transparency film can be used. The pair of slides can then be viewed in an appropriate viewer (or be projected onto a screen). This approach is also used in the famous "Viewmaster" system.

My viewers

There are many other techniques to present the image pair to the eyes. One major technique is anaglyph 3D. It dates back to the early 1850s. Here, the two images of a pair are superimposed into a single image. A pair of color images is first converted to two grey-scale images. One of these is converted to red-scale, the other to green-scale. These monochrome images are then merged. They are viewed with a pair of glasses that has a red lens on the left, and a green lens on the right. Red/green is the standard European color combination, whereas red/blue is more prevalent in the US. Some other color combinations are red/cyan, green/magenta, magenta/cyan, and yellow/blue. There are also grey anaglyphs and color anaglyphs. The latter can normally be viewed OK both with red/blue and red/green glasses. I convert my stereo-pairs (scanned negatives or even scanned stereocards) to color anaglyphs, with a nice freeware software tool called StereoPhoto Maker (see the links section). Anaglyphs have also been used in movies, both in theatres and on TV.

The concepts of the stereocard and anaglyph methods

Another method for projection of stereo images( movies or slides), is polarization. Here, the projector has two lenses, each with a polarizing filter. The polarization of the lens for the left-hand images is 90° different from that of the right-hand lens. The viewer must wear glasses with polarized lenses. The polarizations are aligned with those of the projector. The left eye cannot see the right-hand image (and vice versa), as they have perpendicular polarizations.

Modern TVs (and some movie theatres) use a different technique. Rather than showing both images of a pair simultaneously, they are shown sequentially , in an interlaced manner. Of course, this implies that the left eye is closed (or covered) when the right-hand image is shown, and vice versa. Again, this requires a special pair of glasses. The lenses have LCD-shutters that can be closed and opened. When the left-hand shutter is closed, the right-hand shutter is opened, and vice versa. The shutters have to be synchronized to the TV screen (or the movie projection, or PC monitor screen). Clearly, head-mounted displays (HDMs) that project directly into the eyes do not have the issue of having to prevent each eye from seeing the image intended for the other eye. And of course stereographic images, can be fully computer-generated.

I got into stereography in the early 1990s. I started collecting stereocards first, and then bought a 1940s "Stereo Realist" camera. It uses regular 35 mm negative or slide film. I have made about two hundred stereocards since. Unfortunately, there are no more photo labs that can make monolithic side-by-side prints. Note that older cameras such as the Stereo Realist, use regular 35 mm film, but have a non-standard negative size, and the frames of a pair are not next to each other! So you have to get the film developed - without the lab cutting it (!), and then use a high-quality negative scanner.

My old "Stereo-Realist" camera

For static objects, I now use a digital camera and an inexpensive-but-adequate slider (eBay) on a tripod. The camera can be slid sideways up to 10 cm (4 in.).

My slider

MY STEREOGRAPHIC / 3D IMAGES

Below is a selection of my side-by-side stereographs, both side-by-side stereocards and the associated color anaglyphs. You will need a viewer (e.g., a "lorgnette" glasses) or red/green or blue/green glasses. Higher-resolution images are available on request. To contact me, see the menu at the bottom of this page.