Shutter Speed vs Aperture vs ISO

This article discusses the interaction between shutter speed, aperture and the ISO setting and explains the impact of changing these settings on your final photograph.

Firstly, it is important to note that there is an optimal exposure setting for each photograph you wish to take. Thankfully, this is automatically calculated by your camera (unless you are working with some very old equipment!). You, as the photographer, however, do get the opportunity to choose which camera settings to use at the determined exposure.

The exposure setting comprises 3 variables – shutter speed, aperture and ISO. These can be summarised as:

• Shutter speed – the length of time the shutter is open while taking the photograph;
• Aperture – the amount of light which is allowed through the shutter when it is open;
• ISO – the sensitivity of the digital sensor to light hitting the sensor.

Your camera determines the amount of light which is required to correctly expose the particular scene. You, as the photographer, however, should choose the settings to achieve that exposure.

Thus, for example, the following table shows different settings, resulting in the same exposure:

Shutter speed - Aperture - ISO

1/125s                       f8           100

1/250s                     f5.6          100

1/15s                        f22          100

1/250s                       f8           200

Importantly, each of the above settings would give you a perfectly exposed photograph (in this example). However, how the photograph looks would be different. In example 2, there would be a smaller depth-of-focus meaning the foreground and background would be more blurred. In example 3, there would be a larger depth-of-focus (ensuring front to back sharpness) but the longer shutter speed would blur movement in the picture (e.g. running water) and would likely require a tripod to ensure a sharp end-result.

This is where the fun really starts with photography as you can use the different variables to create different end-results for your photographs, depending on what you are trying to achieve as a photographer.

You will be able to set the different settings on your camera independently or in priority – so, say, you know you want to use ISO 100 and an aperture of f5.6, by choosing the Aperture priority mode and setting the ISO setting to 100, your camera will automatically work out the correct shutter speed. Information on how to select the particular settings should be available in your camera manual.

You should experiment with different settings to get an understanding of the impact on your photographs.

Hopefully useful

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