Stereoimages--a practical approach.

Abstract

In the absence of any aids most people find it easier to cross their eyes than to maintain parallel alignment and thus view the left hand figure with the right eye, since the eyes naturally converge when viewing nearby objects. By accentuating this natural tendency good stereo images can be obtained, except that front and back are reversed and right-handed helices become left handed [8xAmbiguities in stereopsis. Tucker, V. Nature. 1989; 337: 605CrossrefSee all References[8]. This is acceptable for simple line drawings, but if depth cues such as shading or discontinuity in the peptide chain are present then the pseudoscopic image can be confusing. By taking a photocopy and exchanging the left and right diagrams a normal stereo image can be obtained. A useful practical approach to acquiring the technique [9xVisualising molecules without really trying your eyes. Speakman, J.C. New Scientist. 1978; 78: 827See all References[9] is summarized in Box 2Box 2. A further aid, which also provides useful magnification, is an 8 cm diameter (or better 8 ×10 cm) reading lens [10xStereo viewing simplified. Green, N.M. Nature. 1983; 301: 279Crossref | PubMed | Scopus (1)See all References[10]. If the pair of exchanged diagrams is viewed by both eyes through this single lens the amount of convergence required to superimpose the images is decreased by about 30th %. The diagrams should be viewed from about 30 cm and the lens should be moved slowly from the plane of the paper until it is about 10 cm from the eyes. A double image will be seen and, if the eyes are crossed, it will move over and superimpose on its complement as the lens approaches the eye. Often, one image seems almost stationary and the other appears to move, depending on which of the eyes is dominant. Once the images fuse to give the stereo effect the distances can be readjusted to optimize focus and magnification. The use of the lens facilitates crossing of the eyes and, after repeated use, it becomes much easier to obtain the stereoimage without any aid.Table 2Box 2Cross-eyed stereopsis [9xVisualising molecules without really trying your eyes. Speakman, J.C. New Scientist. 1978; 78: 827See all References[9]View the right hand pair of molecules (Figure1Figure1) from about 30 cm and interpose the tip of a pencil 20 cm from the nose. Focus on the tip and move the pencil slowly towards the eyes. The out of focus diagrams will be seen to move together and when superimposed they will fuse to a single stereo image. The eyes may then be refocussed while maintaining the convergence. Repeat the experiment on the left hand pair and note the reversed image and the contradictory depth cues.