Producing Accurate Stereographic Images with a Flashlight and Layers of Glass A Source for Stereopsis via Slides or Overhead Projection Michael J. Strauss University of Vermont, Burlington, VT 05405 Shellie H. Levine University of Maine, Presque Isle, ME 04769
There have been several recent reports concerned with stereoscopic projection and/or preparation of stereographic slides and overhead transparencies for use in the classroom (1-5). All of these suffer from one drawback, the necessary preparation of ~reciselvoriented and scaled stereosconic line drawings of mhecule; using the best viewing angle; When computation facilities are available, one can use ORTEP (6). . .. with the appropriate input of atomic coordinates, layout instructions and a n d a r separation of the stereopair. to eenerate the required images. lf a-large computer is n i t availlhle, one is limited to the drawings papers and hooks (after an ap. in . propriate photographic scaleup).-we report here an extremely simple technique, using only Dreiding or Framework molecular models, a flashlight, small sheets of glass and a piece of cardboard, which produces extremely accurate line drawings of stereoscopic images. Any viewing angle may he chosen, stereo overlays of several molecules in space are easily produced, and any size image can he achieved. In fact, the method is not limited to molecular models hut can he used with any three-dimensional object constructed of connected lines (curved or straight). The simplest possible assembly, using stacks of hooks for supports is shown in Figure I. A flashlight is placed underneath a piece of carhoard so that its beam passes through a small hole (-318 in. diameter). The beam does not need to be carefully aligned, and the hole does not have to he any precise shape. About 20 in. above the carboard is a sheet of glass on which the model is placed. In a darkened room this casts a very sharp two-dimensional projection image of the model on a piece of paper which rests about 5-6 in. ahove the first sheet .ofglass.~,nasecond sheet (Fig. I ).The si7eof the imagr may be changed hy increasing or decreas~ngthe distance between the two sheets of glass. with a pencil on> merely makes a small dot on each atom of the image on the paper, as well as a very light hand drawn line showing which atoms are connected to each other. This line is informational only and does not need to be drawn accuratelv or straight (vide infra). The naner is ,, . then removed and in a lighted room the atoms nrr cunnerred wirha hlack ink ven (fine felt tiuis heir) and asrrairht edw. The pencil is removed with an eraser. ~ c whole e process takes onlv a few minutes. All the stereoimaees shown in Figure 2 weregenerated in this way in about lg min. T o obtain the other stereoview, one merelv moves the flashlieht to a second hole in the rardhoard :>~n.'fromthe f m t (Fii.'l) and repeats the process. I.ookinr down at t hese holes thn,urh the top of the so that they &e parallel with ones eyes, &e hole on the left produces the image for the right eye, and that on the right for the left eye. The hlack ink line images produced may he immediately viewed stereoscopically if they are small enough, when placed side by side to fit in the visual field. With the set-up shown in Figure 1, using Dreiding models, any compact molecules of up to 15 or so atoms can be easily viewed
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directly without reduction. Larger molecules may require n single Xerox reduction of the cast images. Interestingly, by placing one or two more sheets of glass beneath andlor ahove the elass holding the orieinal model. " additional molecules can be introduced and viewed stereoera~hicallvabove or below the orieinal snecies. One nossible orientation for the Michael addition of acetonate to Hcrolein was done this way and is shown in Fieure 2. As noted above, the method is not limited to molecular models (i.e., we have done stereoeraphic proiections of small . . flowers in the same way). All of these views can best be seen in large classes when the images produced are converted into overhead transparencies (blue-line: red-line corresponding to right eye: left eye) using an infrared copying machine and viewing them with hlue-red filters, as described by Crozat and Watkins (7). This method of producing images can be used in any disripline where .?-dimensionalline s
