Exposure Triangle

• A properly exposed image seeks to optimize aperture, shutter speed and ISO. Images that come out too light, too dark or too blurry typically happen when the photographer improperly adjusts one or more of these settings. Overexposed images receive too much light rendering people and objects in the scene too bright. Underexposed images do not receive enough light and render people and objects in the scene too dark. These three settings work hand-in-hand, and a properly exposed image can consist of any combination of aperture, shutter speed and ISO.
  
  

Aperture

• Inside of each lens sits a diaphragm similar to the pupil in the human eye. This diaphragm is called the lens' aperture. The size of the aperture at any given opening is called the f/stop or f/number. The aperture acts as a light regulator. Larger apertures -- the actual size of the opening not the f/number -- allow more light to reach the camera's film or sensor while smaller apertures allow in less light. F/stops are represented as "f/number" for example f/2.8, f/11 and f/5.6. The wider the opening, the smaller the actual f/stop number and vice-versa. This means f/2.8 has a large opening but a small f/number, while f/22 has a much smaller opening but a higher f/number.
  
  

Shutter Speed

• The shutter speed determines how long a camera's film or sensor is exposed to light. A camera's shutter speed range varies, but a typical range is 30 seconds to 1/4000th of a second. Obviously, 30 seconds exposes the sensor to light much longer than 1/4000th of a second. Adjusting the shutter speed also interprets how movement is recorded. Fast shutter speeds stop or freeze movement, while slower shutter speeds render movement more fluid or blurred.
  
  

ISO

• ISO or film speed relates to the imaging media's sensitivity to absorbing light. In the days of film, you selected film based on its ISO speed. Higher ISO films have a higher sensitivity to light and absorb more light onto the film's surface than lower ISO films. Digital camera sensors work the same way except the selections are done electronically and not with film. ISO stands for International Standards Organization, now known as the International Organization for Standardization. Because higher ISO settings absorb more light, a photographer can use a high ISO in low light conditions or when she needs to increase the shutter speed or decrease the aperture size. A typical modern digital camera has an ISO range of ISO 200 to ISO 3,200 but some cameras go as high as ISO 102,000.