The Exposure Triangle

Many people think the magic of photography happens in the camera body, but the true source of magic is light. Photography is all about capturing light. A well-lit subject can be captured poorly, but a poorly-lit subject will never look good.

Therefore, an understanding of the “exposure triangle” is important.

The exposure triangle is how we associate the three variables that determine the exposure of an image. These variables are aperture, shutter speed, and ISO.

There must be balance in all three of these to achieve a proper exposure.

Three factors affect the final image:

1. Aperture: The aperture is the diameter of the lens opening. A wider aperture (lower f-number) means more light because the opening is larger. A narrower aperture (higher f-number) means less light because the opening is smaller. Focal ratios (f-stops) are expressed as f/1.4, f/2.0, f/2.8, f/4.0, f/5.6, f/8.0, etc. The aperture, in combination with the shutter speed, determines the total light that hits the sensor.
2. Shutter Speed: Shutter speed sounds simple enough. And it is. Basically a longer shutter speed equals more light. A faster shutter speed equals less light. Shutter speeds are measured in fractions of seconds. For example, 1/30, 1/60, 1/125, 1/500, 1/2000, etc. To stop the wings of a bird in flight, you need a fast shutter speed of 1/2000.
3. ISO (pronounced eye-so): ISO is typically measured in units, 100, 200, 400, 800, 1600, etc. ISO refers to the sensitivity—the signal gain—of the camera’s sensor. A higher ISO allows you to take photos in darker situations, but the trade-off is grain or noise in the photo.

The Exposure Triangle is the relationship between ISO, shutter speed and aperture. These three components work together to create an actual exposure or photograph. It is referred to as the exposure triangle because when you adjust one element, another element MUST change to capture the same exposure.