ISO is the third and final component of the Exposure Triangle, and in this comprehensive guide, we break down the technical jargon and make it easy to grasp.

Whether you’ve just purchased your first camera or used one for years, there’s one thing we can agree on; learning the fundamentals is overwhelming.

What even is the ISO?!

There are so many camera settings and factors to be aware of, but all you want to do is take a nice photo! Can’t you just stick to shooting in automatic mode and forget about learning the settings?

ISO is a vital aspect of the Exposure Triangle, a collective term that also includes aperture and shutter speed. Understanding these settings and their relationship will give you huge advantages with your camera. It allows you to take complete creative control.

This comprehensive guide will demystify ISO in simple terms, making it easy for everyone who wants to understand this important setting. I’ll explain how the ISO interacts with the other components of the Exposure Triangle to achieve well-balanced images, and you’ll learn some practical applications of the ISO setting, including high and low ISO values and how they impact the photo.

I know it seems complicated, but trust me, it’s not as bad as it feels. With a bit of practice, this will soon be second nature.

So, let’s dive in and learn what ISO is in digital photography:

What is ISO?

So, what exactly is ISO? 

ISO stands for the International Organization for Standardization, but in photography, it refers to a camera sensor’s sensitivity to light. In other words, the ISO setting determines how sensitive the sensor is to light, affecting the brightness and exposure of your photographs. 

The ISO value indicates the sensor’s ability to capture light and turn it into an image. A low ISO setting, such as 100 or 200, means the sensor is less sensitive to light, while a higher value, such as 800 or 1600, indicates a higher sensitivity. 

Understanding ISO is crucial to taking control of your photography and achieving well-exposed and visually appealing images.

The technical aspects of ISO are confusing and, for most, unnecessary to understand. I’ve chosen to simplify some of the explanations to make this as easy-to-understand. I recommend this article from Tutsplus if you want an advanced technical understanding.

Standard ISO Values

The ISO range will vary from camera to camera, but typically they start with the lowest setting at 100 or 200 and double in size as they increase, such as 400, 800, 1600, etc. The highest ISO setting varies and can be anywhere from 3200 to 25600 or even more.

Some cameras go beyond the standard range, offering extended ISO settings, but these can result in increased digital noise and reduced image quality.

How ISO Affects Image Exposure and Brightness

Even though the ISO is a crucial part of the Exposure Triangle, it isn’t actually a part of exposure because it doesn’t affect the amount of light your sensor receives. The ISO determines how brightly the camera renders the photo based on your aperture and shutter speed.  

So while it isn’t a component of exposure, it significantly impacts how bright an image is.

ISO in the exposure triangle

Increasing the ISO makes the sensor more light-sensitive, essentially brightening your photo. This allows you to photograph in darker conditions without sacrificing exposure.

On the other hand, a lower ISO setting decreases the sensor’s sensitivity to light, meaning you need brighter conditions to create a properly exposed photo.

Balancing ISO with Aperture and Shutter Speed

The relationship between ISO, aperture, and shutter speed forms the Exposure Triangle, which determines the overall exposure of your photographs. Adjusting one of these settings affects the others, and finding the right balance is key to creating well-exposed images.

A higher ISO allows you to use faster shutter speeds and smaller apertures, making it suitable for freezing action and increasing depth of field. Conversely, a lower ISO may require longer exposure times or wider apertures to achieve proper exposure.

Understanding this balance allows you to make better decisions in the field by giving your images the proper exposure levels and your creative touch.

Let’s have a closer look at how the ISO works in the Exposure Triangle:

ISO and the Exposure Triangle

Despite not being viewed as a component of exposure, the ISO remains a critical aspect of the Exposure Triangle. While aperture and shutter speed affect the amount of light that reaches your sensor, the ISO determines how bright the image should be based on those values.

The Exposure Triangle Infographic

Achieving a well-balanced exposure involves finding the right combination of ISO, aperture, and shutter speed for a particular scene. For example:

  • In a low-light situation, you can increase the ISO to ensure the sensor captures enough light.
  • In well-lit conditions, a lower ISO setting and a narrower aperture can help you achieve a properly exposed image without overexposure.
  • When capturing motion, adjusting the shutter speed while keeping the ISO and aperture in mind can result in sharp or creatively blurred images.

As you’ve learned from our other articles about the fundamental camera settings, you know there’s always a tradeoff.

Higher ISO values may enable you to shoot in challenging lighting conditions, but they can introduce digital noise and affect image quality (more about this in a minute). Similarly, wider apertures may yield beautiful background blur, but they may also reduce sharpness in certain scenarios.

Experimenting with different combinations of ISO, aperture, and shutter speed will allow you to understand these trade-offs better and develop your artistic style.

Pro tip: Keep an eye on the histogram to make sure your image is properly exposed.

ISO Settings Explained

Now that we have a general understanding of ISO’s role in the Exposure Triangle, it’s time to take a closer look at how the different values affect your photograph. What are the advantages and disadvantages of high or low ISO settings? In what situations should they be used?

Let’s find out:

Low ISO Settings: Advantages and When to Use Them

Photographers often prefer a lower ISO setting for a handful of reasons. When talking about low values, we are referring to the base ISO setting and a few stops up, leaving us somewhere in the 64-400 range (though ideally 200 or lower)

There are three main advantages of using a low ISO:

  1. Image Quality: A low ISO value produces a cleaner image file containing less digital noise. This is especially important when file quality is crucial.
  2. Image Sharpness: Low ISO settings contribute to greater image sharpness and detail, which is ideal when photographing high-texture subjects.
  3. Long Exposures: Low ISO values are well-suited for long exposure photography due to their low sensitivity to light. This popular technique allows you to capture motion in water, clouds, or other moving elements. 

A low ISO should be used when photographing in a well-lit environment or when the camera is mounted on a tripod, and shutter speed is not essential.

Low ISO Setting
An ISO of 64 was used to achieve a longer exposure time

High ISO Settings: Benefits and Limitations

A high ISO value is commonly used to overcome challenging light conditions. I am now referring to values of 800 and up. Here are two of the main reasons to use them:

  1. Low-Light Photography:  When shooting in dimly lit environments or during nighttime, higher ISO values enable you to capture images with proper exposure without the need for slower shutter speeds.
  2. Fast Shutter Speeds: A high ISO value allows you to use a quicker shutter speed to freeze motion. This is typically needed in action photography.

However, there is a downside to using a high ISO:

  1. Digital Noise: As you increase the ISO value, the sensor becomes more light-sensitive and amplifies any signal noise. Simply put, it introduces grainy textures or speckles to the photo, commonly referred to as digital noise.
  2. Image Quality: Due to the increased noise, we often see reduced image quality in terms of detail loss and worsened color accuracy in high ISO photographs.
High ISO Setting
A higher ISO was used to freeze movements and maintain image sharpness when photographing handheld

ISO Noise and Grain: Managing Noise in High ISO Images

Digital noise is something most photographers want to reduce as much as possible, as it negatively impacts the images. So, what can we do to reduce noise even in low-light situations that call for high ISO settings?

Fortunately, there are ways to manage noise and achieve better image quality:

  1. Post-Processing: Noise reduction tools such as Topaz DeNoise AI, DxO PureRaw, or Adobe Lightroom can help reduce noise while preserving essential details in your images. This, combined with smart in-field decisions, will give the best results. However, be cautious not to overdo it, as excessive noise reduction can result in a loss of image clarity.
  2. Shoot in RAW: There are very few reasons why a photographer would not use a RAW file format. These files retain more image data, providing greater flexibility for noise reduction in post-processing.
  3. In-Camera Noise Reduction: Most modern cameras offer a built-in noise reduction tool. You can experiment with this setting to find the right balance between image sharpness and noise reduction. However, I recommend using the two previous methods, as they give you greater control of the process.

What is the Best ISO for Digital Photography?

While the above information helps us understand what ISO is, the real question is what values you should use.

Unfortunately, there’s not one correct setting you should always use. It depends on the subject you’re photographing.

The general rule of thumb is to keep the ISO as low as possible. Ideally, at the base ISO (which tends to be between 64 and 200 depending on the camera)

This should be doable most of the time when photographing during the daytime. The difficulties begin when the low ISO setting requires such a slow shutter speed that you can no longer capture a sharp handheld image. My solution is then to either:

  1. increase the ISO until I reach a desirable shutter speed and aperture or  
  2. mount the camera on a tripod.

But there are times when you need to increase the ISO for other reasons. We’ll come back to this in a minute, but I’ll mention a few scenarios:

  • You’re photographing a quickly moving subject.
  • You want to freeze motion.
  • You’re photographing during nighttime. 

Understanding that increasing the ISO doesn’t come without consequences is important. Using a higher ISO leads to a higher amount of grain/noise in your image, which again can make your image appear less sharp.

Intrudiction to ISO
High ISO gives a lower quality image
Introduction to ISO
Low ISO maintains a good quality of the image

Exactly how much loss of quality you get by increasing the ISO depends on your specific camera. Some cameras can handle high ISO values much better than others.

When to Use High ISO

A high ISO can harm the image quality, but there are many situations where you need to use one. Always use the lowest ISO you can get away with, even if that means a high value, such as 6400. 

Usually, a high ISO is used for photographing:

  • In low-light situations and night photography (both inside and outside)
  • Wildlife or action photography, where subjects are moving quickly
  • Other scenarios where you want to freeze motion (such as photographing waterfalls or waves)

A rule of thumb is to increase the ISO when you no longer get sharp images with your current shutter speed. The extra noise or grain is just part of the game in those situations. 

Night Photography

When to Use Low ISO

The short answer: Whenever you don’t need a high ISO. 

The long answer: Using a low ISO should always be a priority. Exactly how low, as explained above, will depend on the given situation. You should use Base ISO for as long as possible. 

Leave the ISO at 100, and don’t change it until you have to. This could be because the light is fading and you need a longer shutter speed (in which case you should mount your camera on a tripod) or because you need a shorter shutter speed to capture a quickly moving subject.

Mounting the camera on a tripod allows you to lengthen the shutter speed to a duration you couldn’t get sharp images with handheld. This is called long exposure photography

If using a tripod is not an option, you must increase the ISO instead. 

Remember: a low ISO means less noise, which is crucial when making big prints. I can also save you hours in post-production.

Tips for Capturing Low Light Scenes with Minimal Noise:

Higher ISO values become crucial for achieving well-exposed images in low-light situations, such as during dusk, dawn, or indoor photography without sufficient lighting. So, how can we limit digital noise in these situations?

  1. Use a tripod: A sturdy tripod prevents camera shake and is crucial to maintain image sharpness. It also allows you to use longer exposure times, again allowing you to use a lower ISO setting.
  2. Shoot in burst mode: When photographing moving subjects in low light, shooting in burst mode increases your chances of capturing a sharp image. It’s better to have one shot too many than one too few.
  3. Adjust the Exposure Triangle: A wider aperture or slower shutter speed allows more light to reach the camera sensor, meaning you can use a lower ISO setting. It’s important to find the balance between these three settings.

Finally, investing in noise reduction software is crucial. It’s impossible to get noise-free images in each and every scenario, which is part of why post-processing plays such a vital role in photography.


I know that ISO can be a very technical subject, but I hope I was able to explain it understandably. We could go much more into the details, but I don’t see that as a benefit. Especially not if you are a beginner.

The good news is that using the ISO isn’t quite as difficult as you might think initially. With a bit of practice, it will quickly begin to make sense.

Let’s sum things up a little:

  • ISO tells your camera’s sensitivity to light
  • A high ISO leads to more noise/grain in your photo
  • High ISO values are most common when photographing quickly moving subjects, when you want to freeze motion, or when photographing at nighttime.
  • Using a low ISO means a cleaner image file but requires a longer shutter speed

I always recommend keeping your ISO as low as possible, regardless of what you photograph. There is no reason to set it higher than needed.

Are you prepared to have complete control over your camera and capture better images? Let me know in a comment below!

Part 1: Introduction to ISO in Landscape Photography
Part 2: Introduction to Aperture in Landscape Photography
Part 3: Introduction to Shutter Speed in Landscape Photography
Part 4: The Exposure Triangle