​Exposure Triangle

ISO, Aperture and Shutter Speed

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ISO, the aperture and shutter speed are the 3 elements that control the exposure of  your  picture. The 3 working together also control the amount of your picture that is in focus – this is called ‘depth of field’ or DoF.

 

ISO

​The ISO relates to the sensitivity of your camera’s sensor, the lower the IOS the less sensitive the sensor. Usually, the lowest setting is 100 ISO and this is a good setting to start with. The basic settings for the ISO are:

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100    200    400    800    1600  3200

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Many cameras will go considerably higher, however, the lower the setting the less noise or grain, the higher the setting the more noise or grain. The basic rule is – bright light low ISO, dull light higher ISO.

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Aperture​

The aperture works in a similar way to the eye – when light levels are low the iris forms a large ‘hole’ and when the light levels are high it forms a smaller ‘hole’.

The size of the ‘hole’ is recorded as an ‘f’ number. This is determined by the focal length of the lens being divided by the diameter of the aperture. The most common f numbers are:

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F2      f2.8    f4       f5.6    f8       f11     f16     f22

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Every second f number is double and successive f numbers allow only half the light of the previous number. If you go down an f number e.g. f11 to f8 you are doubling the exposure. If you go up an f number, you are halving the exposure.

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Shutter

​The final element that controls the exposure is the speed of the camera’s shutter. A DSLR shutter is composed of 2 ‘doors’. When you press the button, the mirror flips up and the first of the doors, which is in front of your sensor, rises allowing light to hit the sensor. After a set amount of time the second door lowers to cover the sensor thus cutting off the light. Then the mirror flips down. The actual shutter speed is the amount of time between the first door rising and the second door falling. The more common shutter speeds are:

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1/30sec        1/60sec        1/125sec      1/250sec      1/500sec          1/1000sec

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Most cameras will go considerably lower than 1/30sec and by using the camera controls you can hold a shutter ‘open’ for several seconds or minutes. To do this, use the ‘Bulb’ setting.

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Exposure

​The 3 above elements will give you an exposure value for your picture. For example,

ISO 100       @ f8             1/30sec.

However, the following settings will give you the same exposure:

ISO 100       @f5.6           1/60sec

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Lower the f number by one stop, double the shutter speed. Alternatively, you could increase the ISO on the original exposure and either lower the f number by one whole stop or halve the shutter speed, but not both.

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Depth of Field (DoF)

​The expression is used to describe the area of sharpness in your photograph. Whilst your lens and the distance you are away from the subject has an effect on the DoF, the most important aspect to consider is the aperture.

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The larger the f number the greater the area of the photograph that will be in focus; the smaller the f number the DoF will be less.

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At any given aperture, the DoF in front of the subject is only half that behind it.

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Depth of Field

 

 

                              

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