If a perfectly exposed (Ektachrome) colored transparency is held up to a bright light source and viewed through a simple magnifying lens, a three-dimensional quality is obtained. (Lantern slide projection does not give this effect.) A more-than-usual realism is achieved. One gets the feeling of viewing an actual lesion rather than a photographic representation.
Schlosberg has explained that "the phenomenon of monocular plastic depth is due to the release of certain monocular factors from overpowering cues, largely binocular, that show the picture to be flat."
For the purpose of clinical teaching or examination, the three-dimensional effect is especially valuable.
1020 S. W. Taylor St.