We need to quantify light in order to evaluate its intensity, change our camera settings correctly, and then further modify them to brighter or darken a picture. This picture modification is what brings us to the mathematical idea of “exposure value,” which is shortened as EV and is also commonly referred to as “stops.” The intensity of light is its luminance, but even with a value given to luminance, we have no interest in describing it since cameras can catch pictures in any kind of light, or even in total darkness. What we do care about is creating a reference, so that when we change camera settings, we are aware of how those changes will affect exposure and how to correct, if necessary.
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