The best exposure for a photograph is the one that fits your vision. Unfortunately, we have to rely on our camera's light meters to help pick our settings, and as I have written before they don't always give the desired results. To achieve the exact exposure you want, you have to correct for the deficiencies of how light meters work. Luckily, that's exactly what EV compensation is for.
Because the meters built into cameras today average everything to middle gray, you need to tell the camera when it's wrong. That's where EV compensation comes in. With this simple adjustment you are telling your camera it needs to increase or decrease the exposure, and by how much.
Exposure value, or EV, is another way to refer to the brightness of an image, and is measured in stops. With each stop you increase you're doubling the amount of light entering the camera. The opposite is true as well: decreasing by a stop halves the amount of light.
When you look through your viewfinder you will see a small scale on the bottom, usually ranging from -3 to +3 stops. This is the EV scale. Without any adjustments your EV scale will always start out at 0. As you make adjustments the scale gives you the flexibility to let in 1/8 of the light, all the way up to 8 times as much light.
How to Use It
The method of using EV comp varies from camera to camera: on mine it has a dedicated dial, on others you use the cameras rear wheel, and on others it could be in a menu. It would be best to refer to your camera's user manual to find out exactly how to use it, but it should be in a readily accessible place.
EV compensation will work when you are shooting in P, AV, and TV/SV modes. In these modes your camera is picking part of the equation, and EV compensation will give you control over the final results.
Once you have your photo composed, fire off a test shot. By using the results, you can decide if you need to increase or decrease the EV compensation, and how far to move along the EV scale.
As you learn, you'll be able to predict how your meter will react, so you won't need to take the test shot as frequently. Until then, a good place to begin is:
- For a general scene with a mix of bright and dark parts, leave your EV at 0
- If the scene is dark, like a shady forest or dark cove, start at -1 EV to make sure the image isn't too bright
- If the scene is bright, like a snowy field, start with +1 EV so the image isn't too dark
When to Use EV Compensation
All the time! I generally shoot in AV mode, so to make sure I get the photo I intend, I rarely take a photo that doesn't have some adjustment.
Bonus Tip: Bracketing
Another technique you can use to make sure you're getting the best exposure, is bracketing. This is when you take a photo at one exposure setting, and then you take two more: typically +1 EV and -1 EV from the first shot. (i.e. 0 then +1, -1 or +1 then, +2, 0)
Not only is this a quick and easy way to make sure you get a good exposure, but it also helps you learn how to set the EV compensation for different situations. Bracketing is how I learned photography while using film; when you couldn't check the results on the back of the camera, you needed to make sure at least one shot was good!
A Great Tool
EV compensation is a great tool to know how to use. Not only does it help you get a perfect exposure, but it can also help you learn the best settings for different situations. I use it all the time, because short of using manual mode, it's the best way to make the photograph you envision.