Films of Rotating Molecular Models: The Stereoscopic Effect We have recently investigated a method of motion picture photography which offers a three-dimensional effect useful for the illustration of molecular structure with considerably less effort than previous methods of stereo photography.' Other workersa.3 have reported that movies taken by a transversely moving camera often create striking three-dimensional impressions. We felt that equivalent movies of a rotating molecular model taken by a stationary camera would yield similar results and that such films could be used in discussions of stereochemistry and canformatianal analysis. Briefly, the model is placed on a rotating stand capable af rotational periods in the range of 15-60 see. The model should rotate about an axis that is the perpendicular bisector of the film image. Ball and stick models work best, since they show bond angles to advantage and are large enough to embody a number of depth planes. The camera (super-8 works fine) photographs the model against a plain background. For best results, the film strip should consist of a succession of ortho-infinite stereo pairs, generated by virtue of the model's rotation, and appropriate theory' predicts that rotational period and camera focal length should be matched as shown in the table. Flat perspective formulas introducing the rotating examples can be added to pedagogical advantage. Viewing test films under normal ~roiectionconditions convinced us that a stere&copic effect was definite& present. Particularly impressive " FocalLength was an immediate "flattening" of the image that appeared when model and Rotational Perioda rotation was arrested during filming. Students have reported moderate to Focal Length (mm) Period (set) strong 3-D impressions in the absence of any external visual devices. The impression is apparently created by the depth clue of motion parallax. i.e, the differential ho;izantal velocities of image points in the screen 20 24 25 29 plane. 30 35 Enright suggested3 that viewing such films with a neutral-density fil35 41 ter over one eye (the left for clockwise rotation) would enhance the 3-D ef40 fect. He reasoned that a filter would induce a latency difference in the two 45 eyes, causing them separately tnperceive disparate images, i.e., successive 50 59 frames of the movie image. A stimdus of this type would result in true stereopsis and complete three-dimensional vision. The suggestion has preOFor super-8 format, 60.in screen image. cedence in the explanation of the Pulfrich Stereophenomenon.5 a visual effect in which monocular filters cause apparent depth displacements. Many students did report enhancement of the stereo effect when using a filter of about 10% transmittance over the appropriate eye, some of the responses indicating a very strong effect. This, however, occurred most often with eaperienced students, while beginners in organic chemistry, possibly hecause of less exposure to actual models, often reported little enhancement and preferred unfiltered viewing. For this reason we feel the mechanism predicted by Enright does not operate effectively under our viewing conditions, and that filter enhancement most likely accompanies the diminishment of certain binocular clues, such as screen texture and film grain, which would simal a flat screen image. We have thus made three s u p e r 8 films illustrating concepts of conformational analysis covered in our beginning course in organic chemistry. The films each run about 10 min, and they illustrate the usual eonformatianal examples covered in introductory texts. Voice narration over a music background was added via magnetic stripe. We have used the films in our course for majors and student response to content and pedagogy has been very favorable. In view of the simplicity of the photographic method, we feel that the 3-D effects created under a variety of conditions definitely make the films useful for class illustration of structural principles, and that an instructor mterested in visual aids would enjoy trying the technique. The financial support of an institutional grant from the National Science Foundation is hereby gratefully acknowledged. McGrew, LeRoy A,, J. CHEM. EDUC., 49,195 (1972). Cameron, James R., "Third Dimension Movies,'' Cameron Publishing Co., Coral Gables, Florida, 1953, pp. 84-85. Enright, James T., American Serentist, 58,536 (1970). Spottiswoode, R., and Spottiswoode, N., "Stereoscopic Transmission," University of California Press, Berkeley and Los Angeles, 1953, pp. 135-139. 5Pulfrich, C., Naturwiss , 10,553,569,596,714,735,751 (1922). LeRoy A. McGrew Kathy Kitzman Ball Stateuniversity Munice, Indians 47306
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