Description
The name "camera lucida" (Latin for "light chamber") is obviously intended to recall the much older drawing aid, the camera obscura (Latin for "dark chamber"). There is no optical similarity between the devices. The camera lucida is a light, portable device that does not require special lighting conditions. No image is projected by the camera lucida.
In the simplest form of camera lucida, the artist looks down at the drawing surface through a half-silvered mirror tilted at 45 degrees. This superimposes a direct view of the drawing surface beneath, and a reflected view of a scene horizontally in front of the artist. This design produces an inverted image which is right-left reversed when turned the right way up. Also, light is lost in the imperfect reflection. Wollaston's design used a prism with four optical faces to produce two successive reflections (see illustration), thus producing an image that is not inverted or reversed. Angles ABC and ADC are 67.5° and BCD is 135°. Hence, the reflections occur through total internal reflection so very little light is lost. It is not possible to see straight through the prism so it is necessary to look at the very edge to see the paper. The instrument often includes a weak negative lens, creating a virtual image of the scene at about the same distance as the drawing surface, so that both can be viewed in good focus simultaneously.
If white paper is used with the camera lucida, the superimposition of the paper with the scene tends to wash out the scene, making it difficult to view. When working with a camera lucida it is often beneficial to use black paper and to draw with a white pencil.
The camera lucida that commercial comprehensive ("comp") layout artists used from the early 1950s to late 1980s used lenses positioned over a platform where the original reference material (like a photo) was placed. A bellows arrangement and two cranks allowed the artist to expand or reduce the size of the image. The artist could step up and place his or her head under a shade canopy to see the image. The image was projected upward onto a sheet of glass parallel to the floor, where the artist could place a translucent sheet of white layout paper on which to draw. This machine provided the artist a means of quickly and accurately drawing products and of using other photos in the composition.
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