How Does a Digital Camera Work?

A common misconception surrounds today’s digital cameras: Because these cameras don’t use film and because they produce pictures as data files, many folks think that digital cameras must use a radically different method of capturing images. Actually, your family film camera and that power-hungry, battery-munching digital camera you got for Christmas are remarkably similar in most respects.

A film camera has a shutter that opens for a set amount of time (usually a fraction of a second), admitting light into the body of the camera through at least one lens. (Of course, that lens can be adjusted to bring other objects at other distances into focus, or different lenses can be tacked on.)

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As the figure illustrates (up to this point, anyway), your film camera and its digital brethren work exactly the same.

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The big difference is the method that each of these two types of cameras uses to record that incoming light. To wit:

  • A film camera uses a strip of light-sensitive celluloid coated with silver halide, which retains the image. The film must later be developed, and the negatives and positives that are produced can be used (reproduced, usually on photographic paper) to make copies of the photograph.

  • A digital camera, on the other hand, uses a grid (or an array) of photosensors to record the incoming pattern of light. Each sensor returns an electrical current when it’s struck by the incoming light.

    Because the amount of current that’s returned varies with the amount of light, your digital camera’s electronic innards can combine the different current levels into a composite pattern of data that represents the incoming light — in other words, an image in the form of a binary file.

If you’ve read some of my other books on CD/DVD recording, photography, and scanning, you already know about binary, which is the common language shared by all computers. Although your eye can’t see any image in the midst of all those ones and zeroes, your computer can display them as a photograph — and print the image, if you like, or send it to your Aunt Harriet in Boise as an e-mail attachment.

How does the image file get to your computer? That’s a very good question; naturally, no one wants to carry a PC around just to shoot a photograph. Most digital cameras store the image file until you can transfer (download) it to your computer — other digital cameras (and many smartphones) can now directly transfer the photos you take to your PC, or even Facebook or Flickr wirelessly!

Different types of cameras use different methods of storing the image files:

  • RAM cards: Random access memory (RAM) cards (the most common storage method) are removable memory cards that function much like the memory modules used in a USB flash drive. Some memory cards are proprietary, but some cards are interchangeable with netbooks, smartphones, and tablet PCs.

    The most popular types of media include CompactFlash, SmartMedia, and Memory Stick cards, generally ranging from 512MB to 128GB of storage. When the card is full of images, you either download the images from the card (presumably to your PC) to free up space or eject it and “reload” with a spare, empty card.

  • Hard drives: Yep, you read right — some cameras have their own onboard hard drives, and others use tiny removable hard drives that are roughly the same size as RAM cards. Naturally, these little beauties can easily store hundreds of gigabytes of your images.

If you’re wondering approximately how many images you can fit onto a specific RAM card, remember that most 10- to 16-megapixel (MP) cameras now produce images of about 2 to 6 megabytes (MB) at their highest-quality mode.

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