Photography Basics 5 – The Exposure Triangle

Aperture, shutter speed and ISO (covered in the previous three posts in the series) between them determine the exposure.

I’ve listed below some values of each.

Aperture values

f2     f2.8     f4    f5.6    f8    f11     f16

Shutter speed values

4 sec, 2 sec,  1 sec, ½ sec, ¼ sec, 1/8 sec, 1/15 sec, 1/30 sec, 1/60 sec, 1/125 sec, 1/250 sec

ISO

100   200   400   800   1600   3200   6400   12800   25600

Each value either doubles or halves the amount of light hitting the camera sensor than the value either side of it. 

For example:

Changing the aperture from f2.8 to f4 halves the amount of light coming through the lens (yes, it’s counterintuitive, the smaller the number the more light through the lens).

Changing the shutter speed from 1/8 sec to 1/4 sec doubles the amount of light reaching the sensor.

Changing the ISO from 400 to 800 doubles the amount of light reaching the sensor.

Each of these steps individually is known as one STOP. So if you double the amount of light you increase the exposure by one stop, if you halve it you decrease the exposure by one stop.

This means that you can interchange these three sets of values to get the desired final effect. For example if you’re shooting sports you’ll usually need to keep your shutter speed high enough to freeze action (unless you want to show movement). If you want to draw your viewers attention to part of an image you’ll need a wide aperture and to focus on that part. If you’re shooting landscapes you’ll need a small aperture.

Having decided which value is most important you can make changes to one or both of the other  two elements of the exposure triangle to achieve this.

Note that each of the three sets of values are sub divided into one third and two thirds of one stop enabling you to refine your chosen exposure.

The pictures below show how the values of each can be changed although the final exposure (amount of light hitting the sensor) is the same.

If you’d like to know more about this and other aspects of photography there are more details here