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Exposure Triangle: Aperture, Shutter Speed and ISO

By , Saturday 5th December 2015 in Tutorials

The Exposure Triangle is used to illustrate the relationship between the three fundamental elements of exposure: aperture, shutter speed and ISO.

In photography, creating the perfect exposure is a juggling act, balancing aperture, shutter speed and ISO. The trick to balancing the Exposure Triangle is to get all three elements working together so you get the results you want, and not what the camera tells you can have.

The Exposure Triangle

The Exposure Triangle is a triangle which allows you to visualise the relationships between aperture, shutter speed and ISO. As you decrease ISO you have to increase shutter speed or aperture to compensate. The diagram below helps illustrate the exposure triangle.

The Exposure Triangle
The Exposure Triangle

Shutter Speed

Shutter speed is simply a measure of how long the sensor or film is able to capture light. The shutter speed is measured in seconds, tenths, hundredths or thousandths of a second, expressed as 2" (2 seconds), 1/10 (one tenth second), 1/100 (one one hundredths) and 1/1000 (one one thousandth). The longer the shutter is open the more light is gathered.

Aperture

Aperture is the size of the opening in the lens and is generally used to adjust the amount of light entering through the lens. Aperture is measured in f stops or f numbers and the numbers represent the ratio between the focal length of the lens and the diameter of the aperture. These f numbers are typically written as f/2.8 or f/22. Aperture is often used to control depth of field, creating a pleasing background blur to enhance the subject.

ISO

ISO is an International Standard for measuring the speed of color negative film, or how sensitive it is. In digital cameras it is a measure of computed amplification of a digital signal. As with its film counterpart, digital ISO increases the sensitivity to light, at the expense of quality. High ISO film suffers from graininess, while digital ISO suffers from noise during the amplification process.

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About the Author

Tim Trott

Tim is a professional software engineer, designer, photographer and astronomer from the United Kingdom. You can follow him on Twitter to get the latest updates.

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