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ISO shutter speed and aperture relationship explained


I remember the time when I had just picked up a camera with a serious intent to start shooting. It was all so confusing. "So many settings!" I used to keep thinking and then one day I realised that while photographing I could only control the aperture or the shutter speed. I was shooting film, so I had little control over ISO - once the film was inside the camera, it was pretty much fixed at what ISO I was shooting.

So now, while shooting digital, in spite of all the confusion there are just three things you need to control to create a good photograph - ISO shutter speed and aperture (Ok four, if you want to count in white balance too!)

What is the relationship between ISO, shutter speed and aperture?

The relationship between ISO, shutter speed and aperture is also known as the exposure triangle.


These three settings define what the exposure value of a photograph. It means that the exposure value of any photograph can be expressed as a combination of these three settings or values. For example the photograph below was taken at an exposure value of  f11, 1/250th at ISO 100 - where f11 is the aperture, 1/250th(of a second) is shutter speed and the ISO is 100.

iso shutter speed and aperture relationship

So now if I increase the amount of light entering the camera by opening the aperture by 1 stop to f8, the photograph becomes slightly overexposed as seen in the photograph below.

ISO shutter speed and aperture relationship - overexposed

In order to compensate for this, I will have to increase my shutter speed to 1/500 in order to get a properly exposed photograph again. This because I have used another setting (shutter speed) to decrease the amount of light by the same value that I increased the amount of light.

EV valueok500

So, what this relationship primarily boils down to is this:

If you you increase or decrease one of the values in the exposure triangle - you will have to increase or decrease another value BY THE SAME value in order to get the same Exposure Value.

Sounds confusing? Well it kind of does when you put it in words but the good news is that once you see the video below it will become perfectly clear. Please subscribe to our channel by clicking here if you like the video and would like to see more of these.

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