Kaleidoscopes
The kaleidoscope was invented in 1816 by Sir David Brewster. It is a simple optical device in which 2, 3, or 4 mirrors are arranged with one or more edges coincident (aligned) so as to produce multiple images of an external scene. The scene may be a cell mounted at the input end of the mirrors in which colored pieces of glass or plastic are randomly mixed as the kaleidoscope is rotated. Alternatively, an image of an external scene may be focused by an objective lens into the mirrors where multiple reflections of the scene are viewed through an eyepiece.
In either case, several requirements must be met:
- The mirrors should be 8 to 12 times larger than their width to produce the desired multiple reflections.
- First surface mirrors are more expensive than “bathroom” mirrors but they make brighter images that are not tinted by passage of light rays through glass.
- The front lens or the cell that holds the colorful bits of plastic must fully cover the opening within the mirrors.
The two principal mirrors must be aligned precisely to insure a uniform visual display. The angle between these mirrors may be any integral part of 360°, either 60°, 45°, 36°, 30°, etc. A smaller angle produces more reflections and a more complex display, but also requires that the angle be set with increasing accuracy.
Most kaleidoscopes are made as amusing toys or as visual instruments. However, I have made several specifically designed to allow photography of the displays. These instruments include a macro camera lens of short focal length positioned in place of the viewing eyepiece. This lens relays a wide-angle view back into the camera. In designing a photographic kaleidoscope one must keep in mind the difference between this instrument and a telescope or microscope. You look through a telescope or microscope, but you look into a kaleidoscope.
