What is ISO?

What is ISO

The shift from automatic to manual can be pretty daunting for many new photographers…

As you start to get your head around what is aperture and shutter speed, you have camera ISO to contend with and things get confusing again.

There is a lot of misinformation on the internet about ISO. For the purposes of this article, I’m not going to going to get into debates about what is technically wrong or right.

(More often than not, all it does is give you bragging rights in a forum with people you don’t know!)

Instead, I thought it would be better to focus on understanding what is ISO, how it impacts your photos, and how you can leverage it to make your photos better.

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Where does ISO come from?

The term “ISO” is used across countless industries, products and processes so when you hear the term ISO mentioned, it’s not unique to photography.

ISO refers to an industry-standard from the International Standard Organisation. In the case of camera ISO in photography, it is ISO12232:2019.

Camera ISO first appeared in 1974, an output of combining two film standards into one. At the time, ASA and DIN were both film standards so they were combined into a single standard to avoid confusion with users.

What is ISO for?

A sample photo taken at ISO100 on a Sony A7iii that will be used throughout this article to demonstrate the impact of ISO on photographic quality.

Camera ISO’s started as a reference to the exposure sensitivity of a piece of film. What this meant for the photographers at the time, is when the photographer used a higher ISO film, the photograph would be brighter. This gave them an added dimension of flexibility for their photographs.

Although things have changed in the digital world, the basic concept of what ISO does to an image has not changed.

In the film world, ISO refers to the sensitivity of the film. Similarly, in the digital world, ISO refers to the “sensitivity” of a digital camera sensor although that’s not technically how sensors work.

Like their film counterpart, when you have a higher digital ISO, the photo will appear brighter, so it’s easy to think of ISO as a ‘brightness slider’.

As with most things in life, there is no free lunch. Higher ISO’s comes with a price and that price is in the quality of the photo. Higher ISO’s are more grainy and have more digital noise.

Why do we have different ISO settings?

The same composition as above, this time at ISO12800. ISO12800 is commonly needed in low light for professional photography.

We now know that a higher ISO number makes the photograph brighter. That being the case, why do we need different ISO settings at all and why would we want a brighter photo given people take photographs every day at lower ISO’s?

Firstly, the amount of light in our everyday world changes depending on which country we are in, the time of year, the time of day, whether we are indoors, outdoors and whether we have any natural or artificial light available.

On top of that, we have to deal with aperture and shutter speed, all of which impact the amount of light available. This translates to a variety of possible settings to get a correctly exposed image.

As an example, if you were shooting a soccer game in a stadium at night, you would need a high shutter speed to freeze the action. If we were to use a slow shutter, it would blur the players.

On the other hand, setting a 1/1000 shutter to freeze the players’ motion in a dark stadium would result in a black photo due to the low light – this is where using a higher ISO comes to the rescue.

High ISO isn’t confined to sports. As an example, wedding photographers use higher ISO’s to avoid flash and astrophotographers use high ISO’s because the earth moves. That said, ISO is not a once size fits all. Landscape photographers like long exposures which often require very low ISO’s.

Remember, higher ISO’s can reduce the quality of the photo, introducing more grain or more digital noise.

Why use a higher ISO if it’s worse? You can easily fix noise by applying noise reduction  in editing software such as Adobe Lightroom. However, you can’t fix motion blur.

What is high ISO noise and how do I deal with it?

We mentioned that high ISO creates noise, and in most cases, we can deal with it but there are limits.

The below example shows an excessive level of high ISO noise, a photo taken at ISO10,2400 which well beyond the limits for most everyday photographers.

This image was taken at ISO102400 with the Sony A7iii and has no noise reduction applied.

When you start shooting raw, dealing with noise reduction becomes part of image processing.

There are also third-party plugins like Nik Dfine that claim to offer improved noise reduction over in-app functions within Capture One or Lightroom.

However, there are of course limits to what noise reduction can do and it definitely can’t perform miracles.

The below example is the same photo as above with noise reduction applied. It shows considerable improvement over the photo above, however, it is still not good enough for any form of print or social media usage.

Nik Dfine is a third party application for noise reduction, but can’t produce miracles in this case.

If you are shooting jpg and haven’t started raw, your noise reduction should be happening automatically in-camera using specific algorithms.

They won’t be perfect but they should look a lot better than the raw file would look. (See also: RAW vs JPEG.)

What is Auto ISO?

Assuming you are reading this article to learn about ISO, you may already using something called Auto ISO.

Auto ISO is when the camera does all the work for you. It decides what a perfectly exposed picture looks like and adjusts the ISO whilst you can concentrate on the other settings like aperture and/or shutter speed.

The first thing to note here is that there is absolutely nothing wrong with using Auto ISO. The camera systems these days are incredibly complex and intelligent. As a result, Auto ISO is actually pretty accurate for most situations.

Many professionals shoot Auto ISO. I regularly shoot Auto ISO for sports when people are transitioning between very light and dark areas.

The key to learning ISO isn’t about transitioning to manual ISO permanently – rather, it’s about understanding enough about ISO to know when you should use manual.

When you work in situations where light is constantly changing, Auto ISO is often the best solution.

The great thing with Auto ISO is that it works with any combination of manual or automatic settings you define: If you are working in aperture priority it will adjust both shutter and ISO. If you are working in manual, it will only adjust ISO.

How to start using ISO

You are already using ISO whether you want to or not –  it’s actually happening automatically, whether it’s on your camera or mobile phone.

Manually adjusting ISO can be a little intimidating. Full manual mode is a topic in itself, but my recommendation would be the following:

  1. Get comfortable using manual mode with ‘auto ISO’ and ensure you understand the impacts of aperture and shutter speed. Watch how the ISO changes with different environments. This is shown in the viewfinder.
  2. Try using the exposure compensation with auto ISO, then make minor adjustments to the auto ISO if you think the photo is a little under or overexposed. Watch how the ISO adjusts.
  3. Go out on an evening when the light is more consistent and take some photos in manual ISO. If you aren’t sure what ISO to start with, take one photo with auto ISO, make a mental note of that figure, then use that as a baseline when dialing in your manual ISO. As the light starts to fade, you’ll find yourself having to adjust the ISO to keep the photos exposed correctly.

All the above will be a little easier with a mirrorless camera for the simple reason that you can see the photo as it is exposed through the viewfinder.

DSLR users will have to chimp (view the photo after each shot) to see if it matches their expectation.

Final Words

ISO is intimidating but it’s also one of the most powerful aspects of our modern-day cameras. We can shoot photographs in conditions photographers 20 years ago could only dream of.

It is also something you don’t need to be scared of, particularly in the modern era of mirrorless where you can see what your photograph will look like.

At worse, you may get some grainy unusable photos, so if you plan on experimenting, don’t do it at a once-in-a-lifetime occasion.

At best, you’ll learn a powerful new skill and a way to improve your photographs moving forward.

Leave us a comment below to let me know if you found this tutorial on ISO easy to understand.

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Disclaimer: All recommendations are impartial and based on user experience, with no bias to the products or the brand. The products in this post may contain affiliate links.

Athol Hill is a sports and portrait photographer based in Melbourne, Australia

1 Comment

  1. Greg Cromie on September 20, 2019 at 8:31 am

    Great read Athol and highly informative. Well done and cheers.

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