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At left, WoUaston's use of ini<r<)8cope cover slip as a form of caniera lucida; note inversion and lateral reversal of image. At right is shown Amici's use of a prism combined with plane glass.
and the poorest example, is the widely advertised "Magic Art Reproducer," available for under two dollars at many store counters. Using a piece of thin, clear glass and a second surface mirror (silvered on the underside), the Reproducer creates an image so faint that to be used effectively drawing must be done on black paper with white crayon.
The best lucida of the plane glass type is, to my knowledge, not produced commercially. It may be readily constructed by obtaining a small piece of first surface mirror (silvered on the exposed face) and a beamsplitter. Lucidas of the Elane glass type, with or without beamsplitters, ave a basic disadvantage not shared by the prism-type lucidas; differences in eye accommodation may result in the apparent images seeming to resolve themselves above or below the plane of the drawing surface. Correction lenses are available for individuals who note this viewing discrepancy.
Prism-type lucidas have evolved from the time of Wollaston and Amici into a single, triangular 90-degree prism, the hypotenuse-base of which is silvered, itself, or placed on a first surface mirror. The former arrangement is of greatest permanency.
In commercially available form the prism, with faces measuring a scant 3/8 inch, is mounted into a universally adjustable arm attached to a set of telescoping elevating extensions which, in turn, is joined to a form of "C" clamp. The telescoping section bearing the prism supporting arm can be adjusted to tilt over the drawing table and is held to the table by the "C" clamp. In use, the viewer's eye encompasses the reflection through the prism and simultaneously looks down past its edge to see the drawing surface below. Rotating the prism in its supporting-arm permits the image to be seen either right-side-up or upside-down and laterally reversed. The latter can be an advantage if, for example, a person is making a drawing for linoleum block cutting, which calls for backward picture and lettering.
Prisms available from surplus optics establishments, whether silvered or used in conjunction with a first-surface mirror, are generally considerably larger than commercial lucida prisms. This is not a disadvantage; the eye can still look
down past the near edge of the prism to produ^ an apparent image.
All information presented concerning the pris lucida has been predicted upon the standai accepted use of only one eye for the simultaneoi tasks of viewing the object and the drawing su face. Those fortunate enough to have a pair functional eyes are likely to find that it is easi to use one eye to look downward into the ne edge of the prism and the other eye to lo< down onto the drawing surface, allowing tl brain to fuse the two operations into one br liantly "projected" picture on well-lighted pape Greatest ease in drawing the projected image then achieved by adjusting the balance of illun: nation between the object and the paper in manner to suit the individual's preference.
These are sample sketches of three-dimensional subjects made by using the camera lucida.
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Educational Screen and Audiovisual Guide — June, 19('