Educational screen & audio-visual guide (c1956-1971])

lie users may find it advisable to sketch the iginal object on paper by means of the camera cida and then improve upon the sketch by jrking it again on a sheet of tracing paper ced over the first drawing. This procedure most useful where numerous straight lines B embodied in the drawing. Use of a straightge on the tracing paper copy trims up the aparance of the final product. It may be advantageous, also, to put slightly jre light upon the object to be drawn than on the drawing paper. Balancing illumniation a personal matter for greatest ease in drawing hough illumination is not at all a critical aspect the process. While the cost of a commercial camera lucida gins at about 65 dollars, the user can obtain iTy equivalent results from any silvered 90gree prism. For preparing drawings, the scale of existing awings may be readily modified. For example, wall map or chart can be reduced accurately transfer to a mimeograph or a spirit duphcator ■noil. Conversely, a small cartoon may be enged handily for bulletin board use. Out-of-size ustrations in this way become readily adaptable r a multitude of uses. Of perhaps even greater value to the user is s ability, via the camera lucida, to reproduce ree-dimensional objects in graphic form. Landapes, habitat groups, models, mock-ups, people work, hands manipulating objects, artifacts, I are readily reproducible. itf History The camera lucida has been extant for nearly iO years, yet it is surprising how few people low about it, even among audiovisual groups, amera lucidas are covered briefly in the En\clopaedia Britannica and the Encyclopedia mericana. A page of illustrated use is included the Famous Artists Course text. A more recent urce is a four-page booklet available from the dmund Scientific Company, Barrington, New rsey, showing arrangements for making camera cidas using prisms, lenses and mirrors. Comercial lucidas are listed in major art supply talogs and are utilized primarily in commeral art studios. A form of camera lucida was long ed to facilitate drawing through a microscope itil this technique was made obsolescent by the svelopment of photography. The camera lucida was invented by a British ientist in 1818. William Hyde Wollaston desloped lucidas along two basic lines which ■ovetl generic to present-day versions of the inInunent. The two basic lucida principles const of utilizing reflection from a plane glass surur and internal reflection in a prism. W'ollaston's plane glass surface was a microope cover slip. Inclined at a slant of about 45 ' '^rees with the base of the glass being farthest "in the viewer, the surface of the cover slip reivU-d the image of an object to the eye. Simuliiicously the eye looked through the cover slip nto paper below causing the image to appear 1 be projected onto the pai>er. (Figure 1.) In lis instance the apparent image showed itself n the drawing surface upside-down and laterally Bversed. The second or prism type of camera lucida devised by Wollaston consisted of a four-sided prism with comer angles of 90, 67 Va, 67 '^, and 135 degrees ( Figure 2. ) The eye looked vertically down at the position shown, partially intercepting the edge of the prism nearest the viewer. In this manner the single eye saw both the reflected image of the object and the paper below at the same time. The image appeared to merge with the surface of the paper and tracing became possible. If the viewers head inadvertently moved, the "projected" image on the drawing surface shifted position. The image did, however, appear right-side-up and laterally correct. Contemporary with Wollaston, Giovanni Battista Amici combined the prism and plane glass approaches into one. Use of a 90-degree triangular prism in front of an inclined piece of glass permitted the viewer's eye to receive the reflection of the image from the glass after the image had come through the prism (Figure 3). This way the image appeared right-side-up and laterally correct and shifting of the image was minimized. Changes in the camera lucida since the time of Wollaston and Amici have been less in form than in the improved level of performance made possible by newer materials. Developmentally, rather than historically, let us look at some of these adaptations, beginning with the plane glass lucida type. Because the apparent image seen on the drawing surface when clear plane glass was used was extremely faint, attempts were made to strengthen image visibility. Probably in the late 18()0's, someone modified the clear plane glass by applying strips of mirror-reflecting material equally spaced on the glass, in "zebra" fashion. The mirror strips reflected the image more brightly to the eye, which simultaneously looked down through the alternating clear glass strips to see the drawing surface. This ingenious approach was supplanted in time by the beamsplitter. Beamsplitters are pieces of plane glass specially coated to control the transmission and reflection of light. Thev can be made to reflect any given percentage of light while allowing the rest to pass through. The overall surface of the beamsplitter appears clear but its reflecting qualities are so improved that the beamsplitter renders ordinary glass and striped mirrors virtually obsolete. (Mirror-type beamsplitters are a variant in common use in supermarkets, mounted behind meat and vegetable counters. The customer sees only a reflection of the wares in the mirror; employees in the cutting and packaging room in the rear can look through the mirror to see when replenishment of the items is necessary. To this point in the discussion of plane glass lucidas, apparent images appeared inverted and reversed on the drawing surface. This problem was corrected by utilizing a mirror along with the plane glass lucida. The mirror was set vertically, with the bottom edge of the plane glass inclined outward from the mirror. With this arrangement the image reflected from the mirror onto the plane then appeared correctly, in all respects, on the drawing surface. Today, this constitutes the accepted version of the plane glass lucida (Figure 4). The most commonly known lucida of this type. ImjCATioNAL Screen and Audiovisual Guide — June, 1960 275