What Is ISO In Photography, AND How Do I Use It?

by Feb 21, 2024Photography Tutorials

Robin Whalley Landscape Photographer

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What Is ISO In Photography, AND How Do I Use It?

In this article, we explore the ISO setting on your camera and how to use it.

Back in 2015, I published an article titled “Best ISO Setting”. The article you’re now reading replaced that article for a very important reason. A lot of the best advice from 2015 about how to use the camera ISO setting has changed.

Let’s start by understanding what the ISO setting in your camera does.

What is an ISO Setting, and What Does It Do?

ISO is short for International Organization for Standardization. This body sets standards and one of those standards was used originally to measure the sensitivity of film to light. For example, a film with a sensitivity of ISO200 would be twice as sensitive to light as a film with a rating of ISO100.

The light sensitivity of the film was/is very important. It was often necessary to change to a faster or slower film to match the lighting conditions.

This rating system was later carried over into digital photography. But unlike with film photography, we don’t change film. Instead, we turn a dial or change a menu setting. This causes the camera sensor in a digital camera to change how sensitive it is to light.

Let’s take a simple example of a camera with a base ISO setting of 100.

This is the lowest ISO setting available on the camera in question. If we were to increase the ISO setting to 200, the camera sensor would become twice as sensitive to light. Then if we double the setting to ISO400, the sensor becomes twice as sensitive again. It’s then four times as sensitive to light as it was when it was set to 100.

So Why Change the ISO Setting?

As we have established, increasing our camera ISO makes the digital sensor more sensitive to light. The reason we might want to do this is because it affects the shutter speed of the camera.

Imagine a situation where we are using an ISO setting of 100, which produces a shutter speed of 1/15 second. This risks the image we capture not being sharp due to camera shake.

There are, of course, several steps we can take to reduce the risk of camera shake, one of which is to increase the camera ISO setting.

If we increase the camera ISO to 200, the sensor becomes twice as sensitive to light, which in turn doubles the speed of the shutter to 1/30 second. If we then increase the ISO to 400, the shutter speed doubles again to 1/60 second. Continue and increase the ISO to 3200, and the shutter speed increases to around 1/500 second, which is enough to freeze most action.

Of course, the opposite situation can also arise. In Landscape Photography, we often use longer shutter speeds to blur movement. Using a low ISO setting on our camera can help with this.

Slowing the camera shutter speed to capture movement can often be done by lowering the ISO setting

The relationship between the camera ISO and shutter speed is part of what we call the Exposure Triangle and also involves the aperture size.

ISO Camera Problems

But changing the ISO isn’t without problems. Let’s look at an extreme example of what happens when we use a high ISO setting to capture a photograph.

Effect of ISO on a photographic image

Here, we see a magnified section of two images. The one on the left was shot at ISO400, whilst the one on the right was shot at ISO12,800. Notice the speckled effect in the image that was shot at ISO12,800.

This is image noise, which is caused by the increased ISO setting. The higher we push the ISO setting of the camera, the more obvious this noise becomes.

Image noise can completely ruin an otherwise great image, and it’s something that many photographers, especially landscape photographers, try to avoid. This is one reason why we like to mount our cameras on a stable tripod to support them. It allows us to use a low ISO setting to achieve the best image quality.

Whilst this still makes sense, recent developments in photography and AI present other opportunities.

Dealing With Problem Image Noise

In recent years, we have seen some amazing developments in photo editing AI to remove noise and enhance detail. Three good examples that I have reviewed here are On1 No Noise AI, Topaz DeNoise AI and DxO DeepPRIME, which you will find in DxO PhotoLab and PureRAW software.

These products can produce excellent results, with high ISO images appearing noise-free and full of detail.

Knowing that you can now easily remove image noise can be extremely liberating for your photography. Here’s a good example of a tree I photographed in woodland using a Micro 43 camera.

High ISO image processed with DxO DeepPRIME

The image on the left was taken at ISO1600. The deep shadows we see are hiding severe noise, which becomes obvious when we lighten the area. However, the image on the right was first processed using DxO DeepPRIME to remove the noise. Knowing that I could do this allowed me to take the shot handheld. In the past, I wouldn’t have been able to do this as when I lightened the tree trunk it would be full of noise.

Here’s a close-up section from both images with the dark trunk of the tree having been lightened.

Close up of the problem image showing noise caused by the high ISO setting of the camera

The section of the image on the left is filled with noise, while the image on the right, processed using DxO DeepPRIME, is clean.

Having access to capable software allows you a lot of freedom in your photography.

Image Noise Can Look Good

But there’s another development that can help with the image noise problems caused by high ISO settings.

Today’s camera technology has improved significantly over recent years. It’s much better at handling problem noise than it was even 10 years ago. We now find we can use high-ISO settings without producing obvious image noise. In addition, the image noise characteristics of some sensors have begun to look pleasant.

If you use a Fujifilm digital camera, you may also have used Film Recipes.

Fuji has an enviable reputation for the look of its film simulations, and many photographers use these to develop film recipes. These will produce all kinds of beautiful effects, and many take advantage of image noise.

I know of several Fujifilm photographers who like to use Fuji Acros black and white simulations at ISO1600, with noise reduction turned to the minimum. They say the noise produced creates a beautiful grain effect in their images, whilst the high ISO setting frees them to shoot handheld in low light.

So, with that out of the way, let’s look at the answer to the question posed by my original article.

What Is the Best ISO Setting To Use?

With today’s camera technology and software advances, I think we have a new answer to this question.

We need to use the ISO setting that helps us to capture a steady image.

Avoiding camera shake, so that we can shoot handheld in different lighting is now the priority. We should now largely ignore the problems associated with shooting at higher ISO settings. We just need to be ready to apply a software solution to the RAW file when having a noise-free image is important.

It’s also worth spending time to ensure you understand how to use the Exposure Triangle to control shutter speeds and ISO settings.

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