Chi Kwong Changl University of California La Jolla 92037
Projection of Stereoscopic Images by Ordinary Slide Projector
The growing interest in stereoscopic presentation of molecular models in the chemistry classroom has resulted in several recent articles in this Journal (1-4). Both the conventional polarization method of projection of one pair of stereo~ranhicslides throueh two slide . proiectors and the use . of a special prism device to project stereo pairs on one slide throueh a sinele oroiector have been descrihed. Another variacon is the technique of projection of red-hlue (anaglyohv) - . double overlays with an overhead proiector. The anaglyphic method of p;ojection of three-dime&onal images has a n advantaee over the conventional polarization method in that it doesunot require special proj&tion equipment nor a metalized (lenticular) projection screen to preserve the coding of the two channels; thus it is more flexible as far as accommodation of projection facilities is concerned. The author wishes to report an alternative method to prepare an anaglyphic pair of images mounted in a single slide frame suitable for projection from any regular 2 X 2-in. slide projector onto any screen or even white wall to create a true stereo impression when viewed throueh filter elasses. This is most convenient for presenting stereo images without special equipment as these slides can be assorted with other non-stereo slides and presented to the audience through a single projector. It should be ncgted. however. that the anadmhic - - . method is not capable of full-color images; therefore, any part of the stereo imaee one wishes to emphasize should be identified by distinct'symhols rather than colors: This method reauires separate production of the two stereoscopic views on two transparencies of complementary colors and these two transparencies are used together to give an integral stereoscopic image coded in two colors. A special type of color transparency called the diazo film is used to create the colored image^.^ Because commercial diazo films are not intended for direct camera loading, the colored images are best reproduced from black and white master transparencies. T o produce a pair of the initial stereoscopic images, direct phoc&raphy of stcreo line drawings u~inghigh-contrast B&\V a,pv film leg. Kodalith) is recommended since dark and distinct Images will achieve the best result. An excellent source for stereo line drawing* of molecular structures are those Droeram (51 which are generated hv the OH'I'KP romourer . becoming ever more popular and can he found in recent literature concernine inoreanic or biological X-ray crystallography. Ir is important th& while photo>&aphingthe individud memhers of the pair rhe scale facror should he kept the same
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'Present address: Chemistry Department, Michigan State University, East Lansing, Michigan 48824. 2Attempts to reproduce an anaglyphie pair on a slide by direct photography of printed red-blue drawings using various types of color slide films failed to give acceptableresults. The cause is probably due to the unrealistic blue-green color response of most ofthe colored films which distorts the color coding of the stereoscopic channels. %ott Graphics, Inc., Holyoke, Mass. 01040. Diazochrome is the trade name. Each package of Diazochrome contains 25 sheets 8%"X 11"with a cost of about $6.30. 'The success of the anaglyphie method requires that the eolor transmission of the viewing filters he rather carefully matched to the color of the screen images. For best result, the author recommends Roscolene No. 859 (Green Blue) for the blue filter and Roscolene No. 821 (LightRed) forthe red filter, which an available through Edmund Scientific Co., Barrington, N.J. 08007.
so that the relative size of the left-eye view and the right-eye view is preserved. The two negatives are then inverted either by direct inverse photographic processing or by contact printing on another film. The positive images obtained in this fashion are used to print diazo dye transparencies. This is a diazo type process which yields a positive image (6). In principle, an acid stahilized light-sensitive diazonium salt and an aromatic substrate are incorporated into a transparent base. The diazonium group can be decomposed readily by exposure to radiation. In the unexposed area, when the acid compound is neutralized, the undecomposed diaronium salt undergoes a hase-catalyzed coupling reaction with thesubstrate to pro. duce a colored image; while in the exposed area, because the roupling reaction can no longer occur, it remains transparent. The - - .color ..-. - of - - thediarodve isdetermined hv the nature uf both the diazonium salt and the substrate. Most commercial diazo film sunnliers onlv manufacture the hlue colored film hut multipfe'colored fiims can he obtained from Scott Graphics3 The author recommends the use of Diazochrome KRD for the red color and Diazochrome PCY for the blue-green color required in this application. These films are sensitive to uv-blue light and can be manipulated quite safely in normally illummated rooms if they are not subject to direct sunlight or fluorescent lamps. Common contact printing technique is used to print these transparencies: the B&W film being overlaid onbtopof a strip of the diazo film, pressed tightly by a piece of clear glass against a dark flat background, and exposed to light. The sunlight or a sunlamp are satisfactory light sources hut the correct exposure time in either case has to be determined by experimenting with several gradient exposures to afford orooer color density. The exposed strip is then developed in a jar saturated with aqueous ammonia vapor. The right-eye view can be printed in either hlue or red with the left-eye view printed in its complementary color. The two transparencies containing the two views are then trimmed and overlapped with their horizontal coordinates coincident such that the two images almost fuse. With most of the ORTEP drawings where a key word appears in the center beneath each of the two pictures indicating the reference plane, the alignment of the two views is made very simple by superimposing these two words and the best stereopsis will result. The assembled stereo pair is mounted oreferablv in a Kodak Metal Binder since these hinders hold'&ansparekies fiimlv hut do not elue them nermanentlv: .. therefore later adjustment or exchange of frames is possible. These red-blue double image transparencies when projected onto a white background and viewed through red-blue filters produce the stereosco~ici m ~ r e s s i o n .The ~ arrangement of the colored filters s h k l d hecomplementary with the slide (e.g., red filter over the right eye with a hlue right-eye view, etc.); otherwise . a reversed ste;eoscopic dimension would occur. A large quantity of these colored viewers can be assembled in a lorgnette following the suggestion reported earlier (2,3). Literature Cited
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M ~ G & L.A.; J. CHEM. EDUC.. 1s; 195 11972). (3) Cromt, M. M., and Waikins,S. F., J. CHEM. EOUC.. SO, 371 (1973). (4) Ne1son.G.V..J.CHEM. EDUC..SL,47 11974). ( 5 ) Johnson,C.K..ORTEP.OakRidgeNefionslLaborstoryTeehniedReportORNL-3794
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(6) Kosar, J., "Light Sensitive Systems:' John Wile? & Sons, In
