Understanding Exposure Compensation

Your camera can be fooled, learn how to correct your aperture setting

Running under trees.

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Most DSLR cameras 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?

Exposure Compensation

If you look on your DSLR, you will find a button or menu item with a little + and - on it. This is your exposure compensation button.

Pressing the button 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 (exposure value) numbers. By using these numbers, you are telling the camera to either allow more light in (positive exposure compensation) or allow less light in (negative exposure compensation).

Some DSLRs default to 1/2 stop increments for exposure compensation and you may have to change it to 1/3 using the menu on your camera.

What Does This Mean?

Let's say that your camera's light meter has given you a reading of 1/125 (shutter speed) at f/5.6 (aperture). If you then dial in an exposure compensation of +1EV, the meter would open up the aperture by one stop to f/4. This means that you are effectively dialing in an over-exposure and creating a brighter image. 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 faster shutter speed. This will result in your main subject being under-exposed.

By dialing in positive exposure compensation, you will ensure that your subject is correctly exposed. Additionally, by being able to do this in 1/3 increments, you can hopefully avoid the rest of the image becoming over-exposed. Again, this situation can be reversed when there is a lack of light available.

Exposure Bracketing

We sometimes use exposure bracketing for an important, one-chance-only shot that has tricky lighting conditions. Bracketing simply means that we 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.

If you use exposure bracketing, be sure to turn off this feature when moving to the next shot. It is easy to forget to do this. You may end up dedicating the next three images to a scene that doesn't need it or, worse yet, under or overexposing the second and third shots in the next sequence.

A Final Thought

Essentially, exposure compensation can be likened to the effect of changing the ISO of your camera. Since increasing the ISO also increases the noise in your images, exposure compensation almost always represents the better option!

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