1) Your camera tends to over or under expose photos in general. If you think your pictures are always a little to bright or a little to dark, you may want to change your exposure compensation by a notch or two.
2) The majority of your photo is brighter or darker than your subject. Another way of stating this is backlit or spotlighted subjects. Your camera takes a general meter of light and exposure based on the majority of the scene. If your subject is brighter or darker than the overall scene, your camera could easily over or under expose your subject.
(I ended up over exposing the background of the second photo just a little too much)
3) A scenic photo with a bright sky over dark land. Because of the contrast, the majority of the time your camera will properly expose the land but the sky will appear white or washed out.
(You'd see more of a contrast if I had gotten more of the sky in the photos)
4) Snow scenes. Snow is white and highly reflective therefore it tends to get over exposed by cameras. Even if you manage to get a scene that's not overly exposed, it may turn out grey instead of white. (More explaination on that below.)
5) Light on light or dark on dark photos. Examples would be shooting a pale yellow flower against a white background or a black cat sitting on a dark blue sofa. Your tones may end up to be on the grey side vs true white/black. (Read on...)
(Sorry for the bad example but it's the only thing I could find in the middle of the night)
Cameras meter the light of the overall scene and try to expose it to a middle grey tone. Huh? Grey is half-way between black and white. In the spectrum of all the colors, grey is in the middle, therefore it's the color your camera uses as a basis for optimal light or exposure. In the candle photo above, the candle without compensation appears grey because the camera exposed the photo to a middle grey instead of white. Exposure compensation takes away some of that grey tone by telling the camera to over expose the photo. Ever had a beautiful snow scene that turned out grey instead of white? That's why.
Having trouble trying to figure out how much exposure compensation to use? Use your histogram! Don't know what a histogram is? Read my histogram tutorial!
In a nutshell, use positive exposure compensation for:
- backlit subjects
- bright scenes
- highly reflective subjects
- sky scenes
- spot lighted subjects
- subjects against a dark background
- low reflective subjects
- green or dark foliage scenes