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8. ISO

What is ISO?

So now that we’re done with Aperture and Shutter Speed, we’re really getting close to understanding the whole concept behind photography.

There is one more setting left to understand and that is ISO.

Unlike Aperture and Shutter Speed, ISO isn’t a very exciting setting to learn.

However, it is extremely crucial because it makes you understand how all the settings work together.

ISO refers to the sensitivity of the sensor to light.

For instance, let’s assume the following situation:

Let’s say you are shooting at a place where there is less amount of ambient light with the following settings:


Shutter Speed: 1/500

Now you know that both these settings are restricting the amount of light reaching the sensor. Because aperture is set to f22, the aperture opening is very narrow as we saw when we were learning how aperture works. So the amount of light entering the camera is low.

The shutter speed is 1/500, which means the shutter opens and closes in 1/500th of a second, which is very fast. So out of the very less light that came into the camera due to a narrow aperture, even more amount of light gets cut because the shutter closes immediately.

The result is that very less amount of light reaches the sensor.

We know that the sensor absorbs light to produce the image.

Since very less amount of light reached the sensor, the image is likely to be underexposed or dark.

But there’s still a way out.

And that is by changing the sensitivity of the sensor to light. If we can make the sensor more sensitive to light, then it can do its job even with a less amount of light.

So the question is how to increase the sensitivity of the sensor?

The answer lies in changing the value of ISO.

If you increase the ISO value, the sensor becomes more sensitive to light and vice-versa.

This basically means that if you increase the ISO value, it will make your shot brighter and vice-versa.


Relationship Between ISO and Exposure


As seen before, ISO has a simple and direct relationship with exposure. The more the ISO, the brighter the shot.

Similarly if you decrease the ISO number, the shot starts to become darker as the sensor becomes less sensitive to light.

But this comes at a cost. And that cost is referred to as NOISE.

Noise is an annoying phenomenon in photography, which refers to the formation of bad looking grains in the photograph, like in the shot below:

So how does ISO relate to noise?

Relationship Between ISO and Noise

The higher the ISO, more the noise. That means if you use higher ISO values, you will start to get more grains in your shot.

ISO 100, which is usually considered the base (though some cameras can go below that too), results in the cleanest picture as the ISO is the lowest.

Look at the two images below:



If you look at the images, they are almost identical. The exposure of both the images is correct. That means they are of the perfect brightness, not too bright and not too dark.

But there is one significant difference – and that is that the second image contains a lot noise and hence, looks very grainy.

The first image looks nice and clean.

This is because, the ISO used in the first image is 100 and the ISO used in the second image is 6400.

Because of such a high ISO, the image is very noisy and it doesn’t look good.

Hence, in photography, one of the golden rules is that shooting at lower ISO is a good thing and shooting at higher ISO is to be avoided whenever in our control.

Now I know what you are thinking of two things –

  1. If shooting at a high ISO is not good, then why ever do it?
  2. In the images above, shouldn’t the image with the higher ISO be brighter?

The next section on exposure meter will answer both these questions for you.

We’ll also be doing an exercise for ISO, but that is after we learn about something very important – the Exposure Meter and the Tripod, because it will make you understand how Aperture, Shutter Speed and ISO work together.

Next Chapter: How Aperture, Shutter Speed, ISO and Light Work Together