Stereo images create the illusion of 3D by presenting a different view to each eye. The brain deciphers the small parallax differences between each view and reconstructs the depth information.
There are numerous techniques that have been invented to correctly deliver the left and right views from a flat print or display; many require additional equipment such as 3D glasses.
The stereo images on this site are presented as free view pairs meaning that no glasses are needed. The left and right views are shown side by side, and to obtain the 3D effect, you must “fuse” them by making each eye look at the image intended for it. There are two combinations that can be used for free viewing: “wall-eyed” and “cross-eyed”. Most people can’t diverge their eyes, but they can cross them without difficulty, so that is how the stereo pictures are initially presented on these pages. If you are talented enough to free-view directly (the straight ahead wall-eyed mode), or are using 3D prism glasses to help you, click the “view as wall-eyed pair” link on the pages. For the rest of us, follow these directions:
I find the easiest way to fuse crossed-eye pairs is to look at my forefinger, placed directly between the two images (figure 1 above), then continue to look at it as I bring it toward my nose. The pictures will go out of focus, but if you mentally track their positions you will note a
third “image”, the area formed by the overlap of the two, directly between them (figure 2)
When this overlap image looks to be about the same size as the two originals on each side of it, hold that position of your finger. Now comes a rather unnatural maneuver. Without shifting the angle of your view, bring your focus from your finger to the middle (overlap) image. I find the best way to do this is to try to find some object in the image to mentally fixate on (it will be out of focus), then gradually bring it into focus… without having the object split back into its two components. With a little practice, you can achieve this state of dissociated focus, and when you do, you will see the image in 3D! (You have probably never seen constellations like this before).
