The essentials of exposure compensation: what it is good for, how to set it on your camera and which values are common.
Exposure compensation changes the exposure that the camera has metered automatically by a corrective value that you choose yourself to make a photo lighter or darker. It is always a manual intervention and a decision by the photographer.
Exposure compensation not only makes photos look brighter or darker, it also makes colours paler or richer. The brighter example photo was taken with automatic exposure metering, the slightly darker one with a mild negative correction (-0.5; we will come to what such a numerical value means).
Next to that, it helps to avoid overexposure and underexposure. Here a view of the Mediterranean Sea, because of the large darker water surface, the white clouds in the sun are partially overexposed with automatic (multi-segment) exposure metering. Notice how in the darker image (exposure compensation -1.3) more details of the clouds are visible.
Please note: For the image brightness, it is only the final combination of aperture, exposure time and ISO sensitivity that matters. Not how you get there. There are always several ways that lead to the same result. For example, in the second photo I could have tilted the camera up, measured the exposure on the brighter sky and kept it with the exposure lock for my final frame.
Exposure compensation is one tool among others in your camera toolbox; there are different ways and preferences to work with them.
Whether a camera allows the setting of exposure compensation depends on the camera mode. Only one for advanced photography (P, S, A resp. P, Tv, Av with Canon) allow exposure compensation. In M mode, setting exposure compensation has no effect.
Typically, cameras have a button labelled +/- for setting an exposure compensation. Either a dial has to be turned at the same time or subsequently the strength of the exposure compensation has to be set with buttons on the back of the camera.
Some cameras also have a wheel to select the exposure compensation directly.
The setting is made with numerical values such as +1.0 or -1.0 in steps of one third each:
... | -1 | -0.7 | -0.3 | 0 | +0.3 | +0.7 | +1.0 | ...
... | -1 | -2/3 | -1/3 | 0 | +1/3 | +2/3 | +1 | ...
Positive values produce brighter, negative ones darker images.
Smartphones may offer a corresponding selection labelled +/- or ”EV“ on the display.
The numerical values used for setting exposure compensation stand for exposure value, often abbreviated to ”EV“ on camera displays.
Exposure compensation by one light value means doubling or halving the amount of light used for the exposure.
Changing the quantity of light by a factor of...
The setting of an exposure compensation says nothing about whether the brighter or darker exposure is achieved by changing the aperture, exposure time or ISO value. That depends upon the exposure control.
Let's take an example using the exposure mixer, with the numbers shown in the picture. The numerical values for aperture, exposure time and ISO are arranged in steps of one light value each. For an exposure change of e.g. +1.0 one could either
Or choose a mixture, e.g. move each slider up by only 1/3 exposure step. The exact numerical values will be suggested by the camera, you don't need to worry about them yourself.
Now for the exposure control:
And so on and so forth... you can construct as many examples as you like, but they all follow clear rules. If you know the rules of the game, you can handle any other situation yourself.
My indications for the degree of exposure compensation are:
The series of photographs on the right illustrates the effect in steps of 1.0. On the camera display and in an electronic viewfinder you can see a preview of the change in brightness and get a first feel for it. However, a camera display is unreliable for assessing exposures, it is better to be familiar with histograms.