Intro to Photography for Crafters: The Exposure Triangle

Because photography is about light you need to understand how light works inside the framework of a camera. There are three basic components that determines how light is used to create an image. Those three components make up what is called The Exposure Triangle.

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The three main camera settings that create the “correct” exposure and therefore make up the Exposure Triangle are ISO, Shutter Speed and Aperture.  Each of these “ingredients” do different things that allow for the right amount of light, or exposure, to reach the cameras image sensor and capture an image.  You will use these three ingredients to get the correct exposure by mixing and matching them.  There is no single right way to do this but there are rules and guidelines.  The key to getting the correct exposure is to balance the three settings of the Exposure Triangle.  

The Exposure Triangle
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Let’s discuss each component. 

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ISO

The first ingredient in the exposure triangle is ISO.  ISO  represents film sensitivity.   ISO, with film, was used to determine how sensitive a film was to light. Today, and with a digital camera, ISO determines the sensitivity of the image sensor, or how much light hits the sensor when the shutter is fired.   Digital SLR’s allow you to change the ISO at any given moment allowing you to quickly change the image sensors sensitivity to light.  Changing the sensitivity to light allows you to add or decrease light to an image.  

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APERTURE

The second ingredient in the Exposure Triangle is Aperture.  Aperture is the size of the opening of a lens.  The aperture of a lens determines the amount of light which passes through the lens to the image sensor.  Every lens comes with a series of numbers that include the capability of light available to that lens. The aperture is marked by the letter “f.” The “f” represents the largest aperture setting for that lens or how “open” the lens will be.  A lens can have an aperture setting of f/2.8, f/1.4, f/3.5-4.8.  The smaller that number, the more light that will pass through the lens to the image sensor.  The larger the number, the less light that will pass through the lens to the image sensor.  

The aperture also determines what is called the “depth of field” (or Bokeh) of an image or the amount of things that will be in focus in an image.  The larger the number the more things that will be in focus; the smaller the “f” number the less things that will be in focus creating what is called “bokeh.”  Suffice to say, aperture helps determine the amount of light that will pass through the lens to the image sensor creating a sharp image or an image with a large depth of field.  

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SHUTTER SPEED

The third “ingredient” in the Exposure Triangle is Shutter Speed.  Shutter speed determines how long the camera’s shutter is open to allow light to hit the image sensor.  When a camera is fired the camera curtain opens allowing light to hit the image sensor. This light passes through the lens’ aperture before hitting the image sensor.  The shutter closes when the camera is done collecting light.  The speed at which light hits the image sensor is determined by the shutter’s rate or speed.  Shutter speed is represented by numbers that range in seconds from 1/8000 to 30 seconds.  Shutter speeds are measured in a fraction of a second or in full seconds such as in “16 seconds” or “1/125 of a second.”  The faster the shutter opens the less light available to hit the image sensor. The slower the shutter speed the more light available to hit the image sensor.

Shutter Speed also determines movement.  The faster the shutter speed the more you are able to capture a moving object or person and freeze an action. The slower the shutter speed the more blurred the object, person or action will be causing  motion blur.  We will discuss more about how Shutter Speed works in the class on Shutter Speed. Suffice to say, shutter speed determines how much light hits the image sensor when the camera’s shutter is fired determining movement and sharpness or blurriness.  

Putting it all Together

The correct exposure of an image is achieved by mixing and matching the ISO and Shutter Speed on your camera, and the Aperture of your lens. (Note:  You also change the setting for your aperture on your camera but the lens itself determines the “f” stop the lens is capable of achieving.]   Each “ingredient” needs to be in proportion to the other “ingredients” in order for you to achieve the right exposure for your image.  Next time, I will give you examples and ideas on how this works.