Digital Cameras: Dynamic Range Explained
Dynamic range refers to the ratio between the minimum and maximum light intensities; the contrast between black and white. However, we rarely encounter true black or true white in our lives. Everything is somewhere in between this scale. Dynamic range is a very complicated topic, but for the purposes of keeping the concept simple and relevant to photography, we will think of dynamic range in terms of contrast ratios--the difference between the brightest spot of a photo and the darkest spot.
ISO and Exposure
The dynamic range of your camera is dependent on two factors, the ISO and exposure. The ISO setting refers to how much overall light is needed to expose an image. The higher the ISO, the less light you need, however, your photo will lose quality and become grainy. The exposure or aperture refers to how much light is precisely passing through the lens. The more open the aperture, the more light comes through, again at a sacrifice of quality. It is more desirable to add lights as opposed to opening your aperture.
Overexposed and Underexposed
An image is considered exposed when you can clearly see what it is on your display. Once the ISO and exposure are set, you may notice that part of the image seems white from overexposure and other parts are dark from underexposure. What you're seeing is the dynamic range of your image.