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The Science of Photography

by Laurisa White-Reyes

Photography is probably one of the most useful and widely used inventions of the twentieth century. It is a very complex science that involves chemistry, engineering, physics, and artistry. Yet it has become so much a part of our every day lives that we often take its complexities for granted. Today, cameras are "user friendly." Anyone can snap a picture at the touch of a button. But a lot of history and effort has gone into making photography so accessible. Though it is impossible to delve fully into this intricate science here, a brief exploration of it may serve as a sort of lens, providing a limited but rich image of its landscape.

A Brief History of Photography

The Camera Obscura

The word "photography" is derived from the Greek words photos (light) and graphein (drawing). The photographic process was first introduced to the public in 1839. However, the discoveries which paved the way for it began as early as four hundred years earlier with the invention of the camera obscura, which is Latin for "dark room." The camera obscura was simply that, a dark room with a small hole cut into one wall. When light entered the room through the hole, an image of the scene outside appeared on the opposite wall, though the image appeared upside down. The camera obscura soon became a vital tool for artists who were becoming increasingly interested in drawing and painting images that were true to life. As time went on, the camera obscura evolved from a "dark room" to a hand-held box. A lens was added to enhance the clarity and brightness of the images. Additionally, a mirror placed inside would correct the image so that it appeared right side-up. Artists used this device to project images onto paper to be traced. But the images were always temporary.

Then, in the seventeenth century, it was discovered that some substances, including silver nitrate, darkened when exposed to sunlight, proving that images could be formed in this method. Later, at the beginning of the nineteenth century Thomas Wedgwood successfully captured silhouette images on chemically treated surfaces, but the images would fade in sunlight since there was no known method for making these images permanent.

Daguerre and Talbot: The Fathers of Photography

The first successful picture was produced in the summer of 1827 by Nicephore Niepce in France. Eight hours of exposure were required to produce it. Later, Niepce collaborated with Louis Daguerre. Though Neipce died shortly thereafter, Daguerre continued experimenting with photography and soon reduced the exposure time to half an hour. He also discovered that images could be made permanent by immersing them in a salt solution. The French Government purchased the rights to this process, called Daguerreotype, in July of 1839. Though the Daguerreotype quickly became a public phenomenon, it was expensive and images were impossible to reproduce, a problem that was soon rectified.

Earlier that same year another man by the name of William Henry Fox Talbot invented what he called Calotype. Talbot's process required only seconds to produce and allowed for unlimited copies of pictures by developing positive prints from negatives. The quality of the earliest Calotypes were poor in comparison to the Daguerreotype, but the inferiorities were corrected over time and due to its affordability and convenience, the Calotype became the forefather of present-day photography.

Then and Now

The materials used for photography have evolved over time. Originally, pictures were printed on thin sheets of metal, as for the Daguerreotype. Calotypes were printed on specially treated paper. Other methods used glass coated with sensitized egg white (albumen), gelatin and, later, celluloid. Flexible film, similar to what we used today, and the box camera were introduced by George Eastman in the late 1800s. The 1900s saw the development of motion pictures, color photography, and instant cameras. Today digital photography is becoming more and more popular. Who knows what new photographic frontiers lie ahead in the years to come. But no matter where technology may take us, the basis of photography is essentially the same today as it was sixty years ago. All that is needed is a camera and an object whose image is worthy of being kept as more than just a memory.

How Photography Works

"Camera" is a shortened version of the word camera obscura, which is Latin for "dark room," as mentioned earlier. A camera is essentially a box that is dark inside and is comprised of three basic elements: the lens, the camera body, and the film.

The Lens

The lens is a curved piece of glass or plastic which collects and redirects light to a particular point forming a real image. Just as the camera obscura projected an image onto a wall or piece of paper, the lens in a camera projects an image onto the surface of the film. This image looks exactly like the object in front of the lens.

When light waves hit the lens, they bend. A convex lens, where one or both sides of a lens curves out, bends light rays toward the center of the lens converging them, or bringing them together to a single point. In a camera, the lens redirects light rays reflected from the object in front of it and converges it onto the surface of the film behind it.

If the image appears blurred, it is because the light is converging at a point before or beyond the film itself. To make the image clear, or to converge the light right onto the film, the focus of the camera must be adjusted. Focusing simply moves the lens closer to or farther away from the object.

The Film

Everything we see, we see because of light. When light reflects off of an object and reaches our eyes, we see that object as being a particular color, be it red or yellow or blue or any other color. This is because light contains a full spectrum of colors, only some of which are visible to the human eye. These visible colors are those that you see in rainbows or when light is refracted through a crystal.

When light touches an object, most of its colors are absorbed. The color or colors that are not absorbed are reflected making that object appear to be that particular color. For example, a stop sign appears red because the only color in the electromagnetic spectrum which it reflects is red. When an object absorbs all color, it appears white. When it reflects all color, it appears black.

Some materials actually change when exposed to light. This chemical change is called photochemistry. In its simplest form, photography is the process of exposing light sensitive materials to light and leaving an imprint of an object on a piece of film. Film itself is a strip of plastic coated with various substances. Some of these substances are very small grains of silver-halide crystals. Silver-halide crystals are formed by combining silver nitrate and halide salts (chloride, bromide, and iodide). Silver nitrate reacts to sunlight by becoming darker. These crystals are treated with chemicals to make them ultra-sensitive to light, so that when film coated in these crystals is exposed to light, these crystals darken.

Different colors of light travel at different speeds. When the camera shutter opens, it briefly exposes the film to light. Some colors reach the film at greater speeds than others, thus exposing more crystals on that part of the film. The parts of the film exposed to the most light turn dark, the silver-halide crystals change into silver particles and appear black. The areas not exposed remain unchanged and appear white. A latent image is formed on the film, meaning that the image cannot be seen until the film is treated with special chemicals during developing.

In color film, this process occurs in three separate layers of crystals, each layer having been sensitized to a particular color of light: red, green, and blue. Red light forms a latent image on the red-sensitive layer, and so forth. When these layers are developed and overlap, a color image is formed. Black and white film has only one layer sensitized to the light spectrum as a whole which results in images of light and shadow.

The Camera Body

The body of the camera is a sealed box with a shutter which opens and closes between the lens and the film. When the shutter opens, the film is exposed to light. If too much light gets in, too many silver-halide crystals will react and the picture will appear washed out. If too little light hits the film, few crystals will react and the picture will appear too dark. In order to get the picture just right, the aperture (lens opening) and shutter speed (how fast the shutter opens and closes) can be adjusted. Most cameras today do this automatically. The film speed also affects the quality of the picture. The film speed indicates the size of the crystals. The larger the number, the larger the grain. Low speed films are ideal for shots in bright sunlight. High speed films should be used in relatively low light or when the shutter speed must be very fast, as when photographing action pictures.

Film Developing: The Final Picture

Processing film occurs in several steps the first of which involves placing the film in a developing agent which converts all the exposed crystals into pure silver. Next, the film is rinsed with water or a stop bath that stops this process, otherwise eventually all the crystals will turn to silver. The unexposed silver-halide crystals are then removed with what is called a fixing bath leaving the silver behind. Finally, the film is washed with water to remove the processing chemicals. The film is dried and the exposures cut into negatives.

In a black and white negative, the darkest areas are those that were exposed to the most light and contain the highest concentration of silver. On the areas of the film that received no light, the negative contains no silver and is clear. To make a positive image or a picture that looks normal to the human eye, the negative must be reprinted onto photographic paper.

Color film processing differs from that of black and white in that the film is washed with couplers, chemicals which produce a certain color in each of the three light-sensitive layers of film. The film is then washed by a solution which removes all the silver making color negatives appear somewhat orange-tinted. When printed, the processed layers overlap and result in full-color pictures.

Just the Beginning

There is far more to photography than can be shared here. As mentioned earlier, it is a complex science which warrants further investigation. Two resources I found interesting and helpful were the illustrated book entitled The Story of Photography by Giovanni Chiaramonte and translated by W.S. Piero, and the website

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