How to Master ISO in Your Camera

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Ever wondered what ISO actually does to your images? Let’s take an in-depth look at ISO and learn how this basic camera setting can elevate your photography practice.

Words by Urth HQ

What is ISO and What Does it Do?

As we’ve looked at aperture and shutter speed and how they influence exposure, it’s now time to find out a little more about ISO, the third and final corner of the exposure triangle. 

In a nutshell, ISO brightens and darkens your image by increasing and decreasing its level of sensitivity to light. Therefore, ISO is the tool you need for photographing in low light situations or at nighttime. Here’s an example of how increasing ISO increases the brightness of your image.

Shot with ISO 125.
Shot with ISO 400.
Shot with ISO 800.

ISO Definition

By definition, ISO in digital photography is the measurement of light sensitivity. So you would then think the ISO acronym would at least refer to sensitivity but instead, it stands for International Standards Organization.

The International Standards Organization is an actual independent organisation and their standards are internationally agreed upon by experts. Whether it’s in quality or environmental management or workplace, health and safety, ISO (the organisation) brings together the best and brightest minds to develop international standards. Now that you’re aware, chances are you’ll come across other ISO Standards in your day-to-day such as ISO 9001 — a set of criteria for quality management systems.

But ISO hasn’t been around forever. If you shoot film you know that your Kodak Portra 400 film is rated not as ISO but as ASA, which stands for The American Standards Association. Although ASA was replaced by ISO, they are both a linear scale of measurement for describing sensitivity.

ISO 12232:2006 (the full name for the ISO we’re referring to in this article) is the standard that “specifies the method for assigning and reporting ISO speed ratings, ISO speed latitude ratings, standard output sensitivity values, and recommended exposure index values, for digital still cameras”.

Find out all about The International Standards Organization and their camera film speed standard here.

What is the ISO Setting on a Camera

The ISO setting on a camera (ASA on film) controls sensitivity and therefore brightens or darkens your image. As a rule of thumb, you should only increase your ISO when brightening the photo through aperture or shutter speed isn’t an option (i.e. brightening the photo with a slower shutter speed will create motion blur. If you don’t want motion blur, turn to ISO instead).

There are a few other general laws to consider when tinkering with the ISO:

1. Low numbers (i.e. 100, 200, 400) mean low sensitivity

2. Low numbers mean low, or very fine grain

3. High numbers (i.e. 1600, 3200, 6400) mean high sensitivity

4. High numbers mean a high amount of grain or noise 

As with most scenarios in photography, you may need to decide where compromises need to be made. Before setting your ISO in camera, ask yourself the following questions:


Even in the darkest situations, a tripod will allow you to use a very low ISO because camera stabilisation and slow shutter speeds are achievable. This means you can capture fantastic night scenes with very fine grain.


If you’re photographing a crowd of concert-goers and don’t want to create motion blur, you may have to increase your ISO (sensitivity) to enable you to capture an evenly exposed shot at a faster shutter speed. But grain will be your enemy depending on how high an ISO you select.


Grain may be an aesthetic choice, in which case, experiment and find that sweet spot as each camera handles grain differently.

ISO Photos


You can tell if a photograph was taken with a high ISO if you notice a large amount of grain or digital noise. See examples of high ISO photography below.

Shot with ISO 100. Shot with ISO 200.


You can tell if a photograph was taken with a low ISO if the image is crisp with little to no evident grain. See examples of low ISO photography below.

Shot with ISO 1000.
Shot with ISO 640.

Now take a look at these photographs captured of the same scene, one with a high ISO and one with a low ISO. The difference in grain is obvious.

What ISO to Use

Here are some general principles for shooting in the following specific scenarios, and these recommendations are made with the intention of minimising the appearance of grain as much as possible.


ISO 100-400

Generally, you’re going to want your ISO relatively low or at its lowest on a sunny day to ensure you have creative control over the other factors of aperture and shutter speed.


ISO 400-800

Cloudy days are perfect for capturing portrait subjects in a flat and even light. But since this means there is often less light, increase your ISO to ensure your aperture and shutter speed are still calling the shots.


ISO 1600-6400

Setting your ISO for evening or night photography depends on any surrounding artificial light sources. Often when photographing a street scene there will be street lamps and lights in the surrounding buildings, for example, which may influence the ISO you select. 

Again, ask yourself the questions outlined above. If you’re attempting to capture a moving subject, you may want to bump your ISO quite high to allow for a faster shutter speed. If you want motion blur, or to create the red and white trails of passing traffic, you may want to consider using a really low ISO in order to compensate with a really slow shutter speed.

Shot with ISO 1600.


ISO 1600-3200

Astrophotography too depends on external light sources including the moon and other artificial sources. Of course, a full moon is going to light the landscape far greater than a crescent. 

Astrophotography is a game of give and take; finding the right shutter speed to make the stars appear sharp, or finding the right exposure time to create beautiful star trails. Regardless of the creative outcome, it’s always best to start at ISO 1600 and work your way up from there. 

Shot with ISO 2500.

How to Change ISO

Changing your ISO in camera is more difficult than changing aperture and shutter speed. This is because most beginner-intermediate DSLR cameras don’t have a dedicated dial to quickly scroll between ISO settings.

You may need to open the menu or the quick menu (Q button) of your camera to change ISO. But most commonly, there’s a button on the camera near the shutter release that says ISO. If you press this button, your dial previously used to control shutter speed will instead control ISO until a value is selected.  

For beginners, it’s recommended you let the camera figure out the appropriate ISO setting itself. Set the ISO to Auto and keep a keen eye on the ratings your camera designates to each scene as this is a great way to train your ISO understanding. 


ISO is a tool every photographer will need to master at some point. We can rely on our cameras to automatically decide ISO rating but if you truly want to progress your photography, particularly night and astrophotography, experimenting with ISO is a step in the right direction toward having complete creative control over every aspect of your image.

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2021-08-19T05:42:55+00:00Categories: Photography|Tags: |