terminology - What is exposure compensation?

What does exposure compensation do?

If I take a photo with a given shutter speed, aperature, and ISO, and then take the same shot with +1EV or -1EV, what is actually happening?

Is this just a gain control on the sensor?

Can you achieve the same thing by changing ISO?

Answer

Exposure compensation changes the target exposure. Normally the camera is trying to work the settings to get about 18% grey (reflectance), but with exposure compensation of +1EV you are basically just saying to the camera "I want to expose this scene 1 stop lighter than the normal average."

Changing ISO vs Exposure Compensation

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  Manual shooting

  
  
  
  
  • Changing the ISO would have the same effect on exposure that Exposure Compensation would have in AUTO mode. However, so would changing your shutter speed or aperture.
  
  
  
  


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  Automatic modes

  
  
  
  
  • The camera will change either ISO, aperture, or shutter speed as needed to achieve the correct exposure, so adjusting your ISO will only change the shutter/aperture that the camera sets. Changing the exposure compensation will change the target exposure.