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Wednesday, 6 October 2010
the Magic Mirror
Camera = Latin for “room”
Obscura = Latin for “dark”
Go into a very dark room on a bright day. Make a small hole in a window cover and look at the opposite wall. What do you see? Magic! There in full color and movement will be the world outside the window — upside down! This magic is explained by a simple law of the physical world. Light travels in a straight line and when some of the rays reflected from a bright subject pass through a small hole in thin material they do not scatter but cross and reform as an upside down image on a flat surface held parallel to the hole. This law of optics was known in ancient times.
The earliest mention of this type of device was by the Chinese philosopher Mo-Ti (5th century BC). He formally recorded the creation of an inverted image formed by light rays passing through a pinhole into a darkened room. He called this darkened room a "collecting place" or the "locked treasure room."
Aristotle (384-322 BC) understood the optical principle of the camera obscura. He viewed the crescent shape of a partially eclipsed sun projected on the ground through the holes in a sieve, and the gaps between leaves of a plane tree.
The Islamic scholar and scientist Alhazen (Abu Ali al-Hasan Ibn al-Haitham) (c.965 - 1039) gave a full account of the principle including experiments with five lanterns outside a room with a small hole.
In 1490 Leonardo Da Vinci gave two clear descriptions of the camera obscura in his notebooks. Many of the first camera obscuras were large rooms like that illustrated by the Dutch scientist Reinerus Gemma-Frisius in 1544 for use in observing a solar eclipse.
The image quality was improved with the addition of a convex lens into the aperture in the 16th century and the later addition of a mirror to reflect the image down onto a viewing surface. Giovanni Battista Della Porta in his 1558 book Magiae Naturalis recommended the use of this device as an aid for drawing for artists.
The term "camera obscura" was first used by the German astronomer Johannes Kepler in the early 17th century. He used it for astronomical applications and had a portable tent camera for surveying in Upper Austria.
The development of the camera obscura took two tracks. One of these led to the portable box device that was a drawing tool. In the 17th and 18th century many artists were aided by the use of the camera obscura. Jan Vermeer, Canaletto, Guardi, and Paul Sandby are representative of this group. By the beginning of the 19th century the camera obscura was ready with little or no modification to accept a sheet of light sensitive material to become the photographic camera.
The other track became the camera obscura room, a combination of education and entertainment. In the 19th century, with improved lenses that could cast larger and sharper images, the camera obscura flourished at the seaside and in areas of scenic beauty.
Drawing Camera Obscuras with Lens at the top
Most drawing camera obscuras project the image from a lens at the front onto a mirror which reflects it up onto the drawing surface. There are however box and tent insterments with the lens and mirror or a prisim lens at the top that directs the image down only the drawing paper. The artist would sit inside or place his head and arms into openings in the side.
The illustration on the top shows a typical drawing tent in the landscape with a lens of this type on the top. This is an illustration from an 1889 physics book by Steele.
The lens is a 6 1/2" tall, 19th century brass lens for a portable tent camera or box obscura that uses a prism lens to direct the image outside down onto a drawing board inside the tent or box.
The camera obscura in the Outlook Tower at the top of the Royal Mile, next to the castle was established in the 1850's by the optician Maria Theresa Short and was originally known as Short's Observatory. The optics were replaced in 1947.