Kim Fyson Photography

The Exposure Triangle

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The triangle refers to the three inter-related variables the photographer can adjust to control the amount of light entering the camera to expose the photograph. With modern cameras, it is really easy to master the use of these three variables.


Adjusting the shutter speed  controls "movement" in the picture, freezing motion (using a fast shutter speed) or creating the illusion of motion (using a slow shutter speed to blur movement)

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Adjusting the aperture controls the depth of focus in the picture (also known as depth of field) allowing you to maintain focus in depth with a small aperture, or to create an out of focus area, (usually behind the main subject but not always) to isolate the main subject and reduce superflous detail in the surroundings.

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ISO is a variable associated with the sensitivity of the camera's sensor.  This setting has a bearing on the clarity of the photograph  and is adjusted to faciliate photography in a wide range of light conditions. A setting of 400 ISO will cover most situations but in very bright light, or in the studio 100 or 200 ISO will give the finest results.  If light is dim 800, 1600 or higher ISO will enable shots to be taken but the quality may be somewhat degraded.  With modern cameras, setting the camera to Auto ISO should give you the best setting for the prevailing light conditions.

(more about sensors)

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In the graphic below you can see how adjusting each of these parameters changes the result and can be used creatively.

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How to choose your settings

First decide which is more important depth of focus or control of movement then set either the aperture or shutter speed appropriately.

Can you achieve the correct exposure with these settings?  If yes then take the picture,  if no then increase the ISO setting.  If you have set the camera to Auto ISO then it will make this final choice for you.

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