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How Does a Digital Camera Work?

Just how does a digital camera work? How can a small device with no film capture such amazing images?

A digital camera looks like a traditional film camera and it appears to do the same thing - take photographs - but the technology within that little hand held device couldn’t be more different.

Photography with a film camera was very much a mechanical and chemical process. Cameras didn’t need a power source (although later models often had battery operated film winding mechanisms and lens drives) and images were captured by allowing light to land on a chemical coated film which then had to be treated with other chemicals to reveal the image.

A digital camera allows light through an aperture in much the same way as a film camera but the light is focused on a semiconductor which records the images electronically.

The digital image captured is in a format that makes sense to the computer on board the camera. The computer records the image as a whole load of tiny colored dots - pixels - that fit together seamlessly to make up the complete image. Without getting too technical, the light waves are converted into a digital format.

The semiconductor that receives the light through the lens will either be a CCD, a charge coupled device or a CMOS, a complementary metal oxide semiconductor. Both act to convert the received light into electrons - they turn light into electricity. The difference between the two semiconductors is perhaps not a matter for discussion here as ultimately they produce the same end result. What is worthy of note is that cameras with the CCD technology tend to use more power than CMOS, which can affect battery life.

In order to determine colors digital cameras use a color filter array which breaks the incoming light down into red, blue and green pixels and uses interpolation in order to make an educated guess about true colors. The more expensive the camera the more sophisticated this filtering process is and the better quality the resulting images.

The amount of light entering the camera is controlled by two mechanisms; the shutter speed and the aperture. There really is no difference between film cameras and digital cameras where these mechanisms are concerned.

Once you decide what you want to photograph, you aim your camera at the target subject (duh). Depending on the camera, there may be an autofocus mechanism whereby the lens will focus automatically once the shutter button is depressed halfway. There may also be a zoom function allowing you get a close up shot of something in the distance.

Once the camera has focused the image, completely depress the shutter button. There is a reassuring mechanical “click” noise built into most modern cameras, even though the process is not mechanical.

When the shutter is open, light streams into the camera and is focused on the CCD or CMOS. This is converted into an electrical charge and the computer processor and filter interpolates what color each pixel should be. These pixels are then displayed on the LCD for you to view and decide whether or not the photo is what you want or needs to be shot again.

The images are stored on a memory card or chip until such time as they are downloaded for permanent storage.

From the photographer’s point of view, there is much about digital photography that is similar to film photography. But in case you are ever asked ‘how does a digital camera work?’ you now have a better idea.