Exposure Compensation is an important camera setting that helps you control the amount of light entering the lens. It over rides the exposure setting automatically selected by the camera.
Exposure compensation should be used when light is very bright and there is high contrast in a scene. It is also useful when subjects are back lit. When a subject is back lit, a digital camera can be fooled and expose for the light behind the subject. As a result, the subject will appear too dark.
The human eye is capable of seeing detail in both dark and light areas of a scene. However, digital cameras have a more limited range. Under some lighting conditions a photo can be either under or over-exposed. In these situations, the Exposure Values can be changed to help improve the overall exposure.
Exposure Values (EV)
Selecting an acceptable Exposure Value helps preserve detail in both dark and bright areas of a photo.
In high contrast scenes, photographers usually under expose so the brightest areas are not blown out (ie. washed out and contain no detail). Dark areas generally retain detail better than bright areas. An under exposed image can usually be edited to pull out details in the darker portions of a photo.
Exposure Values are numbers that refer to various combination of lens aperture and shutter speed. The values are measured in “steps,” typically between (+) 2 EV through (-) 2 EV in increments of 1/2 EV or 1/3 EV.
Decrease the EV if photos appear too light (overexposed). Increase the value if photos are too dark (underexposed).
Exposure Compensation
Exposure Compensation can be changed manually using a digital camera’s Exposure Compensation button or menu. This lets you to override the metered exposure by a value between a range of [-] 2 to [+] 2 EV.
How settings are adjusted varies according to a scene or subject, and direction of the light falling on the subject.
Digital Single Lens Reflex cameras and some compact digital cameras can be set to bracket for exposure automatically. The camera takes a series of three or more shots at differing exposures.
Photos illustrating changes using different Exposure Values
Back-lighting
The three shots on the left, were taken with the source of light coming from behind the subject. This is known as back-lighting.
Front lighting
The images on the right were front-lighted.
In both examples Exposure Compensation was used by changing the Exposure Value +.07 and -.07. Other Exposure Values could have been used such as -1, -2 or, +1 +2.
Notice how more detail in preserved when using certain Exposure Values. The goal it to retain as much detail as possilbe in the darker areas, while not causing the photo to be totally underexposed.
Detail in dark areas can be brought out when editing. But if an area is blown out, it is devoid of detail and no amount of editing can restore it.