The term »camera«, as well as the apparatus itself, derives from
»camera obscura«, which is Latin for »dark room« or »dark chamber«.
The original camera obscura was a darkened room with a minute
hole in one wall. Light entering the room through this hole projected
an image from the outside on the opposite, darkened wall. Although
the image formed this way was inverted and blurry, artists used this
device, long before film was invented, to sketch by hand scenes
projected by the »camera«. Over the course of three centuries, the
camera obscura evolved into a handheld box, and the pinhole was
fitted with an optical lens to sharpen the image.


PREHISTORY OF PHOTO-OPTICS

As early as the fourth century BC (circa 336-323 BC), Aristotle described a method for viewing a solar eclipse without damaging the eye. If a metal plate punched with small holes was held up to the sun, he said, then a corresponding image of the sun could be projected through it and onto the ground. The method was not novel to Aristotle, and likely well established before he wrote about it. This simple optical principle is the foundation of photography.

In 1038 AD, an Arab scholar named Alhazan described a working model of the camera obscura. Literally meaning dark chamber, the camera obscura was a room or box lit only by a small hole that admitted sunshine. Light rays poured through the hole, eerily assembling an image of the outside world on the opposite wall.

Although Alhazan did not actually construct the device, his work would influence a medieval tinkerer named Roger Bacon. In 1267 AD, Bacon created convincing optical illusions by using mirrors and the basic principles of the camera obscura. Later, he used a camera obscura to project an image of the sun directly upon an opposite wall.

Throughout the middle ages, Bacon's ideas were adapted for astronomical observations of the sun. The camera obscura became a popular tool for safely studying eclipses.

It was not until the Renaissance that the instrument was widely used as a drawing tool. Although Leonardo Da Vinci is popularly credited for using the camera obscura to draw, that is only partially true. A student of physiology, Da Vinci built a small camera obscura to test his theories about the workings of the human eye and the concept of perspective. Da Vinci never used the camera obscura to draw. Without a lens, the camera was not a very effective or portable tool for viewing the world.

The introduction of the orbem e vitro, a kind of primitive biconvex lens, revolutionized the utility of the camera obscura. Like the lens that C.C. Harrison and J. Schinitzler would perfect in 1860, the orbem was constructed of two convex lenses. The design reduced distortion and increased clarity. Although no inventor is known, the lens was first mentioned by Girolamo Cardano, a Milanese mathematics professor, in the 1550 edition of his scientific encyclopedia.

In 1558 the Neapolitan scientist Giovanni Battista della Porta suggested the camera obscura would make a wondrous aid to artists. In his Magiae naturalis, he discussed the applications to portraiture, landscapes, and the copying of other paintings. With the lens, he wrote, "You will see everything clearer, the faces of men walking in the street, the colors, clothes, and everything as if you stood nearby."

Another notable improvement came in 1568 when Daniele Barbaro, a Venetian nobleman, described a camera obscura outfitted with a lens and diaphragm. This forerunner of the aperture could be made progressively smaller so the image would become ever sharper. With continuing improvements in optics, the camera obscura no longer needed a large, stationary room to create an image.

In 1572 Friedrich Risner constructed a small hut that could be carried around the countryside and used to make topographical drawings. Camera obscuras began to shrink in size and improve in optical quality. By 1657, camera obscuras were small enough to be carried under one arm. During the latter half of the 17th century, they proliferated across Europe, with uses as varied as painting, architectural drawing and spying.

As remarkable as the instruments were, they didn't fully satisfy the needs of artists. While canvas painting is a vertical pursuit, many artists preferred to sketch a scene on a laptop pad. In 1676, Johann Christoph Sturm, a professor of mathematics at Altdorf University in Germany, introduced a reflex mirror. Mounted at a 45 degree angle from the lens, the mirror projected the image to a screen above. This elegant configuration is at the core of modern single lens reflex cameras.

In 1685, Johann Zahn, a monk from Wurzburg, solved the final piece in the optical puzzle. Improving upon Sturm's design, he introduced lenses of longer and shorter focal lengths. Scenes as wide as a landscape or as close as a portrait could be viewed with a simple change of lens. He also painted the interior of his camera obscura black to avoid internal reflections. Excepting a mechanical shutter, Zahn's invention was the prototype for today's camera. Yet it would be over one hundred and fifty years before the camera obscura and photosensitive chemicals were combined to make permanent photographs.


PREHISTORY OF PHOTO-CHEMISTRY

Not too many years after Friedrich Risner carted his portable camera obscuras across the countryside, Dutch scientist Angelo Sala began experimenting with curious substances called silver salts. In a pamphlet published in 1614, Sala noted that when powdered silver nitrate is exposed to the sun, "it turns as black as ink." It is significant that Sala never distinguishes whether it is the sun's light or its heat that produced the reaction. It wasn't until 1725 that Johann Heinrich Schulze, a professor of anatomy from Nuremberg, solved the mystery.

While attempting to make phosphorous, Schulze discovered a chemical that created the opposite effect. He noticed that a piece of chalk dipped in silver-tinged nitric acid turned purple when exposed to the sun. The unexposed side remained white. At first he thought this was due to heat, but trials by fire produced no photographic effect. After a number of experiments, he discerned that a solution of silver nitrate exposed to light turned black. In dramatic demonstrations he used stencils wrapped around bottles of silver nitrate to create crude photographic impressions. The Imperial Academy at Nuremberg was amused but not overly impressed by his exhibition, and Schulze did not pursue his study.

Espionage and the need for covert communications advanced photochemistry to the next level. In 1737 Jean Hellot, a Frenchman associated with the Academy of Royal Sciences in Paris, proposed a method of secret writing by photochemical methods. Using weak silver nitrate solution as ink, letters composed by dim light remained invisible until exposed to sunlight for a few hours.

Images made from silver salts were far from permanent. In 1777 Carl Wilhelm Scheele, a Swedish chemist, discovered that blackened silver chloride was insoluble in ammonia. But silver chloride that had not been exposed to light dissolved in ammonia. This suggested that an image made from exposed silver chloride could be "fixed" or made permanent by washing the unconverted silver away in an ammonia wash.

Fascinated by the relationship between light and photo-sensitive silvers, Scheele continued to make important discoveries. Exposing a sheet of silver-chloride coated paper to the solar spectrum, he noticed that some rays blackened the paper more quickly than others. Violet, for example, turned the silver dark almost instantly, whereas red took nearly 20 minutes. This observation would play a vital role in making accurate photographic exposures.

Photography's further metamorphosis owes a small debt to the butterfly. Tom Wedgwood, son of the famous potter Josiah Wedgwood, was an avid botanist. He collected specimens from across the natural spectrum, but was frustrated by their ephemeral quality. He wanted a permanent record of his collection.

In 1796 he unknowingly picked up where Scheele left off, and began experimenting with silver salts. Coating paper and leather with silver solution, he pressed leaves, fibers and butterfly wings against the sensitized surface. The resulting photo grams were in one sense the world's earliest photographic images. Unfortunately, they were far more delicate than even the most fragile butterfly wings. Had Wedgwood known about Scheele's research, he could have fixed his pictures with ammonia. Working in vain with a variety of soaps and varnishes, Wedgwood abandoned his pursuit in 1802.