Exposure in photography is a crucial element that determines the image that is recorded on the image sensor of the camera. Three adjustable parts control this exposure. These are the ISO, shutter speed, and aperture.

Exposure Triangle

ISO Speed is the sensitivity of the camera’s sensor to light. Each of the rating’s values represents a light “stop.” Each of the incremental ISO numbers represents a doubling, when higher, or a halving, when lower, of the sensor’s light sensitivity. Aperture determines the diaphragm of the lens, which controls the amount of light traveling through the lens and to the film plane. The f-number indicates the aperture setting, with each f-number representing a “stop” of light. Shutter speed is the speed with which the curtain will open and close. This is measured in mere fractions of a second.

The combination of these elements represent an EV, or given exposure value, for a given setting. Any change of any of the trio of elements will reveal a specific and measurable impact on the way the other two parts react. An increase in the f-stop decreases the lens’s diaphragm size, for example. Reducing the speed of the shutter impacts the way motion is captured.


The value of ISO ratings ranges from 25 and up to or over 3200. This indicates the particular light sensitivity. A smoother image results from a lower ISO rating because the image sensor is less sensitive, producing less digital noise.


The aperture of the lens is the diaphragm’s opening; this determines the degree of focused light that passes through the lens. At an f-stop of f/2, an enormous amount of light goes through. This is true even in a fraction of a second. At its smallest, perhaps at f/22, only the barest amount of light is permitted in.

Shutter Speed

Shutter speed has its measurements in fractions of seconds. It indicates the speed with which the curtains of the film plane close and open. Shutter speed is responsible for controlling how long light can enter the lens to hit the film plane or image sensor. It enables the photographer to capture images in split seconds.