Getting the Right Exposure

How brightness of a photo is determined by the Exposure Value (EV) of the camera. The process of evaluating the amount of light and shutter speed / aperture size required by the camera is known as metering. The appropriate setting is then defined as 0 Exposure Value. Increasing or decreasing the Exposure Value thus alters the brightness of the photo by changing the shutter speed or aperture size. The process of altering the EV value of a camera is known as Exposure Compensation.

Each unit advancement in EV value is known as a "stop". Usually EV values are adjustable in stops of 1/3 EV. Increasing the EV value by a full stop doubles the amount of light entering the sensor. Therefore the shutter speed halves or aperture size and ISO doubles, or any combination to give a +1 EV.

In short, ISO 200 1/60s f/5.6 and ISO 100 1/30s f/5.6 has the same EV value. So does ISO 200 1/120s f/2.8 and ISO 400 /120s f/5.6




For compact cameras, the exposure compensation setting can easily be accessed by the menu button. With the initial EV value of 0, the shutter speed was 1/52s. Increasing the EV compensation to +2/3 EV results in a slower shutter speed of 1/30s, and the image is brighter assuming aperture size is kept constant at f/3.5 . The reverse applies.


As for DSLR, the exposure compensation can be accessed via the +/- button and seen through the viewfinder. It will be reflected in the exposure bar in the viewfinder in steps of 1/3 EV. As shown in the photo below.



Intially at 0 EV, the shutter speed was 1/40s. Increasing the exposure value by 1 stop indicated by the exposure bar results in the shutter speed being halved. Decreasing the exposure value by 1 stop doubles the shutter speed.