Almost all digital cameras have an Exposure Value (EV) Compensation setting. This setting is needed because the camera can sometimes make incorrect assumptions about the lighting of a photo. Changing the EV will make sure your photos are always correctly exposed.
Why Do We Need Exposure Value Compensation?
Your camera is calibrated to expose images correctly for scenes that have a mix of dark and light areas. This works well in most situations because our images normally tend to have brighter areas (sky) and darker areas (shadows). On Auto, the camera chooses a brightness setting around mid way between the brightest and darkest areas and makes sure that area is correctly exposed.
This causes problems, however, when all of your image is very bright (like a white sandy beach or snow), or very dark (like deep green forest scenes). For very bright scenes, like at the snow, the camera thinks the very bright part should be the 'mid point'. This causes the snow to appear gray (because it's mid way between white and black). Similarly for darker images.
How To Use EV Compensation
EV Compensation helps to fix this by telling the camera to expose at a higher or lower setting than it thinks is right. For very bright settings (like the snow or beach), set an EV value as a positive number (+1/3, +1 etc). For very dark scenes, choose a negative EV number.
Now, I know what you're thinking - that doesn't make sense! If the subject is very bright, don't I need to set a lower EV (negative number) to make sure the image is exposed correctly?
Well, no. It's the opposite. It helps to think of what the resulting image will look like. In the snow, where there are lots of bright areas, the camera will choose a mid point in the bright area, so the snow will look gray in the resulting image. To fix that and make the snow white (as it should be), we need to brighten the image. Thus we need to increase the exposure and use a positive number.
The same with very dark subjects. The camera will choose a very dark point as the mid-point so everything will appear too bright in the image. We need to lower the exposure (negative number) to compensate.
Even if you know the direction (+ or -) to set the EV, it's harder to judge how much to compensate. My suggestion is to try different values and check using the LCD screen after each until your photo looks right (not too many very light or dark points).
Some cameras can even do this automatically (Called Auto Exposure Bracketing). I don't recommend using this as YOU will be a much better judge of a correctly exposed image than your camera.
Use Your Camera's Scene Modes
If you don't want to worry about exposure value, check to see if your camera has scene modes. The Beach and Snow scene mode automatically sets the appropriate EV compensation so these images won't appear too dark.
Surprisingly, changing EV is a great way to capture stunning sunsets. The sun tends to mess with the exposure as it's a very very bright spot (even at sunset). The camera tries to compensate and sets a higher exposure. This darkens the rest of the image and destroys any of the colors in the sky.
To get the colors back, set the EV to +1 or +2. This will increase the exposure which will lighten the rest of the image, and bring the colors back!
Use Exposure Value Compensation when your scene is all very bright, or all very dark. Use positive numbers for bright scenes and negative numbers for dark scenes. Experiment with different numbers until your image is correctly exposed.
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