Print ThisHow Does Photographic Film Work?
A Bit of History
One of the earliest colour photos was created in 1877 by Frenchman Louis Arthur Ducos du Hauron. To make the photo he had to take three separate photos using different colour filters, develop the photos on different gelatins containing colour pigments and then superimpose the images to create one final colour image.
Public Domain
The discovery and invention of photographic film starts with one of those wonderful events in science: a complete accident. In 1727, a German scientist named Johan Heinrich Schulze was mixing a batch of silver nitrate when he discovered something amazing. Exposing the silver nitrate to light made it turn purple!
Schulze found that by cutting out letters and affixing them to his flask, he could make letter shadows on the solution, areas that wouldn’t change. Only the parts of the solution exposed to light would change colour in this way.
Other scientists took Schultze’s discovery and tried to make practical photographic film by dipping paper into the solution. The problem, though, was that the image wasn’t “fixed”. That meant that once the film was taken out into the daylight, it all turned dark, effectively blacking out the image.
Almost a hundred years later, scientists learned that a chemical with a mouthful of a name, sodium hyposulfite, could remove the unexposed silver in a “darkroom” before it was exposed to light. With that discovery, photographic film was born.
How It Works
Black and white film has one light sensitive chemical emulsion sandwiched between transparent coatings.
by David Garrison
Photographic film is photosensitive — it changes its properties when it’s hit by light. The trick of the photographer is to expose only certain parts of the film to the light. That’s the reason the camera goes “click” — the camera’s shutter is opening and closing very quickly to let in just a little bit of light to impact the film. That’s also why photographers develop their film in a “dark room” — they don’t want any extra light impacting the film until it is “fixed”. Keep that door closed!
Light has energy. If you’ve ever gotten a sunburn, you know about the energy of light. That energy can affect the silver compounds on the film, just as light affected the silver nitrate in Schulze’s flask so long ago. In black and white film, the silver compound either reacts to light or it doesn’t. In colour film, there are three separate layers of silver compounds — one compound each for red, green, and blue light.
Colour film has three chemical emulsions, each sensitive to a different colour of light.
by David Garrison
Once the film is exposed, it’s locked away in the dark until it is developed. The developing process involves lots of chemistry, too. First, the film is stabilized. The image on undeveloped film is extremely faint — too faint to see, in fact. The stabilizing solution reacts with the silver compounds to make the image visible. After rinsing off the stabilizing solution, the developer next places the film in the fixing bath. The chemicals in the fixing bath react with the unexposed silver compounds, leaving only the image behind. After this step, the film is no longer sensitive to light. Now you can open the door.
Going Digital
One of the biggest benefits a digital camera has over a traditional film camera is the ability to review the photos you've taken.
by Keith Lamond
After learning some of the complex chemistry behind photographic film, it’s sort of a shame that film is becoming more and more rare. But digital photography has some big advantages. A digital image doesn’t have to be developed; instead, it can be sent straight to a computer, e-mailed all over the world, or stored in electronic memory for as long as you like.
Think of a digital camera as lots and lots of individual solar panels — thousands or even millions of them. When light enters a digital camera, instead of activating chemicals on the film, it releases a tiny electric current in a photocell. All the electric currents in all the photocells add up to a single digital image.
For Further Information
The Kids' Guide to Digital Photography: How to Shoot, Save, Play With and Print Your Digital Photos by Jenni Bidner (2004). Learn how to make the most of your digital camera with this book.
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, and creating backgrounds.
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 lot more.