Most DSLRs provide exposure compensation, allowing you to adjust the exposure measured by the camera's light meter. But what does that actually mean, and how do we apply it in practical photography terms?
Read on to learn the answer to the question: What is exposure compensation?
What Is Exposure Compensation?
If you look on your DSLR, you'll find a button or menu item with a little + and - on it. This is your exposure compensation button. Pressing it will bring up a line graph, labeled with numbers from -2 to +2 (or occasionally -3 to +3), marked at increments of 1/3. These are your EV numbers. By using these numbers, you are telling the camera to allow in more light (positive exposure compensation) or less light (negative exposure compensation).
What does this mean in practical terms? Well, let's say that your camera's light meter has given you a reading of 1/125 (shutter speed) at f5.6 (aperture). If you then dial in an exposure compensation of +1EV, the meter would open up the aperture by one stop to f4. This means that you are effectively dialing in an over-exposure. The situation would be reversed if you dialed in a negative EV number.
Why Use Exposure Compensation?
Most people will be wondering at this stage why they would want to use exposure compensation. The answer is simple: There are certain occasions where the light meter of your camera can be fooled. One of the most common examples of this is when an abundance of light exists around your subject ... for example, if a building is surrounded by snow. Your DSLR will most likely try to expose for this bright light by closing down the aperture and using a faster shutter speed. This will result in your main subject being under-exposed.
By dialing in positive exposure compensation, you'll ensure that your subject is correctly exposed. And, by being able to do this in 1/3 increments, you hopefully can avoid the rest of the image becoming over-exposed. Again, this situation can be reversed when there is a lack of light available.
I sometimes use exposure bracketing for an important, one-chance-only shot that has tricky lighting conditions. Bracketing simply means that I take one shot at the camera's recommended meter reading, one at negative exposure compensation, and one at positive exposure compensation. Many DSLRs also feature an Automatic Exposure Bracketing function (AEB), which will automatically take these three shots with one click of the shutter. It should be noted that these are normally at -1/3EV, no EV, and +1/3EV, although some cameras allow you to specify the negative and positive exposure compensation amounts.
Essentially, exposure compensation can be likened to the effect of changing the ISO of your camera. Because upping the ISO increases the noise in your images, exposure compensation nearly always represents the better option!