How Does a Camera Work?

by Stephen Whitt, September 1, 2008

A Bit of History

"View from the Window at Le Gras" is the first permanent photograph and was taken by Joseph Niépce in 1826.

Public Domain

Cameras have changed a lot in the past 400 years. “Camera” means “chamber”, and in fact the first cameras really were chambers. Artists used the camera obscura, or pinhole camera, to project an upside-down image of a brightly-lit scene onto a canvas. The artist could then trace the outlines of the scene.

The next step is to remove the artist. Was there a way to make the image permanent? If you’ve read about photographic film, then you know about the first efforts to permanently record images made by light. Inventors such as Joseph Niépce, Jacques Daguerre, and William Fox Talbot all made advances in recording images, and each of these advances changed the form and function of the camera.

In 1900 you could have purchased a Brownie for just $1.

Public Domain

Cameras really started to change the world with the introduction of the “Brownie” camera in 1900. With the Brownie, photography was no longer just for professional photographers; the average family could now own a camera. Snapshots, spontaneous, and un-posed images started to record everyday life. This miniature camera was inexpensive and easy to use, and versions of the Brownie were still being sold into the 1960s.

Digital cameras are beginning to change photography at least as much as the Brownie did over a hundred years ago. With digital photography, not only can pictures be taken at will, but they can be downloaded to a computer and sent all over the world with just a few clicks of the mouse.

How It Works

Every camera is essentially a lightproof box, with some method of letting in just a small amount of light at just the right time. Once the light is in the box, it forms an image (like in the camera obscura), causes a chemical reaction on photographic film (like in the Brownie camera), or energizes a photocell (like in a digital camera). To find out how the light gets in to do its thing, let’s imagine what happens when you snap a picture, maybe of a dolphin playing in the surf. (You can see right away that a camera obscura wouldn’t do you much good for this kind of picture!)

When you press the button on an SLR camera, the mirror flips up exposing the film to the light coming through the lens.

by David Garrison

One kind of camera — which can be either a digital camera or a traditional film camera — is called a single-lens reflex (SLR) camera. In this camera, there is only a single set of lenses for both viewing and photographing an image. Let’s say you spot your dolphin and lift your camera to your eye. What happens?

First, light bouncing off the dolphin passes into the camera, through a set of lenses, and onto a mirror. From there, the light bounces up and into a funny-shaped piece of glass called a pentaprism (penta means five, and the pentaprism has, you guessed it, five sides). Once light enters the pentaprism, it bounces around in a complicated way until it passes through the eyepiece and enters your eye.

The dolphin is swimming just below the water, but you have a feeling it’s about to surface. Wait for it, wait for it…there! You snap the picture. When you press the button on the camera, the mirror flips up out of the way. Instead of bouncing into the pentaprism, light from the dolphin passes directly to the back of the camera. There, it either hits photographic film and starts a chemical reaction, or else it impacts an array of light-sensitive cells that release a tiny electric charge in each activated cell. Either way, even though the dolphin’s long gone, you’ve captured its image. Congratulations!

SLRs are not the only camera type. Many of us use direct vision compact cameras or just “compacts”. In this camera, the lens for viewing is separate from the lens we use to take photographs. Because of the two sets of lenses, compacts don’t need a pentaprism or a hinged mirror, making them smaller and lighter than the SLRs.

Camera Facts

The flash on a camera is our attempt to light up a scene that’s too dim to show up well either on film or electronically. Flash bulbs once could only be used for a single flash, because they actually burned a metal called magnesium. The magnesium burned with a brilliant white light, made even whiter by a bluish filter that covered the glass around the bulb. Modern flash cameras use a very strong electric current from a battery. The current moves through ionized xenon gas, causing the gas to glow white.

Food For Thought

Build your own camera obscura to recreate the history of the camera.

by David Garrison

Your camera obscura will work best on a sunny day.

by David Garrison

Even though they’re an ancient technology, camera obscuras are still popular among hobbyists. You can build your own camera obscura using nothing more complicated than a round oatmeal box and some wax paper.

Cut the oatmeal box to make two equal-sized tubes.
Stretch a piece of wax paper across one circular opening of the box and tape it into place.
Now tape the two tubes back together, so that the wax paper is inside, in the middle. Use heavy tape (black if you have it) to block out all the light.
Make a tiny pinhole in the round bottom of the box. Hold your eye up to the big opening at the top. Allow light to pass through the pinhole. For example, a skyscraper on a bright, sunny day is a great object to photograph.

What you’ll see is a miniature, upside-down image on the wax paper. Think about the way the light rays move, and you’ll quickly discover why the image is upside-down.

For Further Information

The Kids' Guide to Digital Photography: How to Shoot, Save, Play With & 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.