The Over and Under on Exposure
The Over and Under of Exposure
How does your camera know what the correct exposure is? Your camera's exposure system evaluates light reflecting from your subject and selects an aperture value and shutter speed combination that will represent your subject in an approximate average tone (not too bright and not too dark).  Pros refer to this as “18% gray.” This works well for almost all your shooting situations except when your subject happens to be darker or lighter than an average tone. This is where it is helpful to apply the following rule of thumb: (-) exposure compensation darkens the image; (+) exposure compensation brightens the image.

Exposure Compensation:

Exposure instructions
EV Step located within your camera's customization menu permits you to set the interval to either 1/3, 1/2, or 1 full stop increments. EV step menu


Overexpose for lightly toned objects or subjects that dominate the scene:

Apply exposure compensation on the (over) plus (+) side.   
Camera's Exposure Image with +1 Exposure Compensation
house dark house correct

Underexpose for darker toned objects or subjects that dominate the scene:

Apply exposure compensation on the (under) minus (-) side.  
Camera's Exposure Image with -1 Exposure Compensation
Cats Light Cats Correct

Although we are using white or black objects in the above examples, the same principle can be applied towards colored subjects. For example, you may need to underexpose to show the true deep blue of an afternoon sky.

Camera's Exposure Image with -1 Exposure Compensation
Sky Light Sky Correct

If you are unsure whether to apply -1, -2, etc., take a few shots and download them to a computer to evaluate which gave you the best image.

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