Photographic Film

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How Does That Work?

Photographic Film: A Bit of History

In 1827 a Frenchman, Joseph Niépce, took the first "picture". He put a metal plate covered with a chemical called bitumen into a camera box. The bitumen got hard on the parts of the plate exposed to the sun. When the plate was washed, a permanent picture remained. It took Niépce eight hours to expose his photograph!
     Louis Jaques Daguerre built on Niépce's work. "Daguerreotypes" (as they were called) were made on sensitized metal plates placed in the camera. The plate was later developed in mercury vapour (a potentially deadly process for careless photographers).
     In England, William Talbot also experimented with the new art of photography. But he was going about things a bit differently. Instead of making positives on metal plates, Talbot made negatives on paper. While Talbot's pictures were not as clear as Daguerre's, they were reproducible. Talbot's originals were called "negatives" (the area most exposed to the light was the darkest); the pictures made from them were called "positives" (the area most exposed to the light was the brightest).
     Since the nineteenth century many people have worked hard to cut down exposure times and to develop new types of film. In the 1890s, George Eastman's roll-film camera made it possible to load a camera once and take a series of pictures. Today, we can load a pre-packaged roll of film into a camera in seconds. Thanks to one-hour photo processing, we can have our film developed soon after.

How It Works

Black and white film is made up of a chemical mixture (called an "emulsion") protected by a thin plastic layer. In colour film, the emulsion is made up of layers sensitive to blue, green, and red light. When you take a picture, the film's chemical coating is exposed to the light.

     The emulsion is made up of millions of silver salt crystals (called "silver halides"). When the film is exposed to light (as the picture is being taken) these crystals break down into black silver. If you tried to look at the film now, you wouldn't see much because the amount of silver created is very small.
     In the first step of the developing process, chemicals are used to enhance the images on the film. The developing chemicals break down more crystals into silver. Once the image is visible, the film must be treated so it is no longer sensitive to light. This is done with another chemical which converts the remaining silver halides into colourless salts. The film is then washed and dried.
     The photo is made by passing light through the negative onto light-sensitive paper. The process you started when you snapped a photo of Fido is complete.

Film Facts

Self-developing film is made up of over 12 layers of light-sensitive chemicals and filters. After a picture is taken, the film moves through rollers, breaking open a capsule full of developing fluid. The developed picture pops out in a few minutes.
     The world's most expensive photograph was sold for almost $400,000 (US)! The photo shows artist Georgia O'Keeffe's hands.
     The oldest photograph, taken by Frenchman Joseph Niépce, dates to 1827.
     The longest negative on record measured seven metres! It was produced in 1992 and showed 3,500 people at a concert in Austin, Texas.

For Further Information

If you want more information about film and cameras, focus on:
     Photography Basics: An Introduction for Young People by Vick Owens-Knudsen (1983). A short but informative introduction to photography. It includes how to photograph different subjects, darkroom basics, and tips for double exposures and motion shots.
     The Photographer's Handbook by John Hedgecoe (reprinted 1992). Just about everything a serious enthusiast needs to know about cameras and photography. This book covers flash techniques, lens types, perspective, photographing people and wildlife, creating backgrounds, etc.
     Photography: Take Your Best Shot by Terri Morgan and Shmuel Thaler (1991). An introduction to how a camera works, composing good pictures, light, action shots, animals, colour, special effects, and the darkroom.
     The Young Photographer's Handbook by George Haines (1984). All-around introduction to photography: how cameras work, lenses, choosing the right film, camera care, understanding light, how to photograph a "ghost", writing with light, capturing fireworks, and a whole lot more.