It’s in every camera manual and in thousands of photography tutorials online; so why mention it? Because so many photographers don’t know how much it will improve their photography.
In your camera’s green Auto (or Idiot…) Mode, the camera does everything for you. This is great, but it also means that you don’t have much control. Your photos might be too dark or too bright but your camera doesn’t give you the option to over-rule its thoughtless calculation. But with the other modes, you can take back control and make pictures that are closer to your artistic vision.What is Exposure Compensation?
Exposure compensation allows you to make your pictures brighter or darker.
Your Exposure is the combination of Aperture (size of the hole), Shutter Speed (how long the hole is open for) and ISO sensitivity (how much the camera amplifies the signal to brighten the picture) that determines how bright your picture is.
Photographers used to set the exposure manually by choosing a film with a marked sensitivity such as ISO400, then the aperture and the shutter speed to get the ‘right’ exposure for the brightness of the part of the scene they were photographing. You can still do this with many cameras in Manual Mode (M) but happily with digital cameras you can now change ISO sensitivity without changing films. Because you manually control the three things that determine exposure (aperture, shutter speed and ISO sensitivity), the exposure compensation won’t adjust the brightness.
But when the camera calculates the exposure for you, you can use the Exposure Compensation button and dial to adjust it, making it brighter (+) or darker (-). In Program Mode (P), Aperture Priority Mode (A or Av) and Shutter Speed Priority Mode (S or Tv), the camera still chooses the aperture, shutter speed and ISO sensitivity, but you now have the option to compensate for its calculation/guess, which makes the picture brighter or darker. This is Exposure Compensation.
For more info on the exposure modes, we recommend this article;
Digital Camera World: Exposure Modes