Sometimes it seems like pure magic to capture a moment in time in a still photograph. Exactly how does a camera preserve that split-second moment for eternity? Let’s take a look at the inner workings of the common single-lens reflex (SLR) camera.

A camera basically consists of a lightproof box that lets in a bit of light at just the right moment. Once the light enters the camera, it creates an image by causing a chemical reaction on photo film.

Of course, SLR cameras can also create purely digital images without using photo film at all, but we will concentrate on the traditional use of film today.

Let’s imagine you’re taking a picture of your dog playing in the snow. As you see your dog running toward you, you lift the camera to your eye.

Outdoor light reflects off your dog, bouncing into the camera, through the lens and onto a mirror. The light then bounces off the mirror into a five-sided piece of glass called a “pentaprism” and into the eyepiece.

Finally, the light passes through the eyepiece and into your eye. This allows you to see the image exactly as it will appear on film.

As you hold the camera to your eye, you wait for just the right moment. Your dog stops for just a moment and snap! You’ve got your shot.

When you press the button on a camera, the mirror flips out of the way. Light then passes onto the back of the camera where it hits photographic film and starts a chemical reaction.

When you click the button, you instantaneously record the reflected light off objects in the camera’s field of view. Though you probably can’t tell, film consists of a thin sheet of plastic coated with tiny silver crystals in a gelatin. The crystals react to light that passes through the camera and onto the film.

Once you’ve captured your photo, it’s time to develop the film in a darkroom. The development process involves dipping the film in several chemicals. Special chemicals called “developer” help the image become visible.

If you have ever held developed film up to the light, you may notice that something looks strange. Developed film gives you a negative image! This means dark objects will look light and light objects will look dark.

When it’s time to print your photo, you must shine a light through the negative film. This creates a shadow on special photosensitive paper, leaving an image that is the opposite of the negative — a positive print! At last you have your photograph.


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  1. it will never cease to amaze me the things that people come up with, still baffled by the idea that we have the ability to freeze an image, a moment of our life in a picture, i just…!!!!! what we see is in our hands a few seconds later, amazing

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Have you ever wondered…

  • How does a camera work?
  • What is film made of?
  • How do you develop film into a finished photograph?

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Ready to make a first impression? Even without a camera, you can make a photo by using light from indoor lamps or even the rays of the sun.

Experiment by placing different objects on special photosensitive paper to find out what kinds of interesting and beautiful patterns you can capture on your solar-powered prints. Visit to learn how to buy this special paper, get more suggestions for fun activities using this paper and visit the gallery to see other people’s works of art.


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Learn how to tell a story with the pictures you take. Visit National Geographic Xpeditions’ Photojournalism Guide.


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