Camera Obscura
  The Camera Obscura is a 19th century optical device often used by artists to make quick sketches in the field. A competing device is the Camera Lucida .

   "Camera Obscura" means "dark room", and the use of a pinhole in a window blind to form an inverted image of an outside scene on an opposite wall of a dark room has been known since at least the time of the Arab scholar Ibn al Hait[h]em (or Alhazen, ca. 956-1038). The replacement of the pinhole with a converging lenwas first described by the Venetian, Daniel Barbaro, in 1568. He suggested that the image would be improved by covering it with a disk having a small hole in the center, a very early reference to stopping down a lens to increase the depth of focus.

   The box form of Camera Obscura shown at the right was invented by Johann Zahn in 1685. This example is in the historical apparatus collection at Transylvania University, and is of the form used by William Henry Fox Talbot for his experiments with photography in the 1830s.

   The Camera Obscura below is is in the collection of historical apparatus of the National University of Ireland in Galway. It was used for sketching; the tracing paper was placed on the missing glass inside the folding hood, and a 45° mirror inside the box reflected the image onto the paper.

 REFS: Thomas B. Greenslade, Jr. "Nineteenth Century Textbook Illustrations XXI: The Camera", Phys. Teach., 16, 162-163 (1978) and Reuben E. Alley, Jr., "The Camera Obscura in Science and Art", 18, 632-638 (1980)

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