Aperture, Shutter Speed and ISO

They work together to create an exposure and affect your image in different ways.

If you missed the individual articles you can find them here:

Aperture  –  Shutter Speed  –  ISO

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You can change the level of brightness in a photograph in these 3 different ways:

  • Aperture – How much light passes through the lens
  • Shutter speed – How long the sensor is hit with light
  • ISO – How much the processor amplifies the light collected by the sensor

Each will affect your image differently:

Aperture affects depth of field

aperture

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Shutter speed affects movement

shutter

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ISO affects noise

iso

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One increment in any of these scales will either double the amount of light or halve it.  This is known as ONE STOP.

Let’s take a look at aperture.  We are going to start out at f/5.6

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If we close the lens one stop we only have 1/2 of the light.
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If we close the lens 2 stops then we only have 1/4 of the light we started with.
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Now if we open the aperture of the lens 1 stop we will have twice the amount of light,
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and if we open the aperture 2 stops we have 4 times the amount of light.

The same principal applies to the ISO and shutter speed scales.  If we have an shutter speed of 1/250th of a second and we change it to 1/60th of a second then shutter will be open 4x the amount of time and our image will be 2 stops brighter.

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This exposure is ONE STOP too bright.

ISO 400       f/16      1/250 sec

How can I correct it?

I can lower my ISO one stop, close my aperture 1 stop, or shorten my shutter speed 1 stop.

ISO 200       f/16      1/250 sec

ISO 400       f/22      1/250 sec

ISO 400       f/16      1/500 sec

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All three elements work together in your camera to create the exposure.

The Exposure Triangle

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The Rule of Equivalent Exposures

If you cut the light by half in one way, you must double it in another to retain the same level of brightness.

Let’s say that for a correct exposure my camera meter reads:

  • Shutter speed of 1/15 of a second
  • Aperture of f/2.8
  • ISO 1600

But I know that I need a shutter speed of at least 1/60th to be able to hand hold my camera without shake.

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I have three options to get to 1/60th of a second and keep the same exposure brightness in my photograph.

There is two stops of light loss by going from 1/15th to 1/60th, and I must gain that light back in another way to compensate and keep my exposure correct.

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I can raise my ISO 2 stops to 6400

But I don’t want the noise that ISO 6400 will create, so I will look at changing my aperture.

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I can open my aperture 2 stops to f1.4

And I think that f/1.4 would be too shallow of a depth of field,

So maybe a combination of changing ISO and aperture would work for me.

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I raised my ISO 1 stop to 3200 AND opened my lens 1 stop to f/2

I was able to get the 1/60th of a second that I wanted and retain the proper exposure.

 Aperture, Shutter Speed and ISO

They work together to create an exposure and affect your image in different ways.

You as the photographer get to choose every aspect of your photographs.

Be creative 🙂

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All text and images by Melinda Walsh

www.mlnda.com

To learn more about The Exposure Triangle check out our classes at Action Camera

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