Either you’ve just purchased your first camera or you’ve 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? I mean, the photos don’t look that bad. Right?

The truth is that there’s a reason why your favorite photographers have all taken the time to learn this. Knowing how to operate your camera gives you more flexibility than you would have otherwise. That is what allows you to get more creative.

I know it seems hard but trust me, it’s not as bad as it feels. With a little practice, this will soon be second nature and you’ll be able to capture even better images than what you are right now.

The ISO is one of the three fundamental camera settings and the one that will do the most damage to your image files if not used correctly. So, let’s take a deep breath and take a closer look at ISO in digital photography:

What is ISO?

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

While it might not be technically correct, the most common way of explaining the ISO is by saying that the ISO expresses your camera’s sensitivity to light or measures the sensitivity of the image sensor.

This means that a higher ISO value makes the camera more sensitive to light, while a lower value makes it less sensitive.

In other words, the higher the ISO you use, the quicker shutter speed or narrower aperture you need in order to get a correctly exposed image. A low ISO means the camera is less sensitive to light and you need a longer shutter speed or wider aperture.

You can think of the ISO as a waterwheel. When ISO is low, the waterwheel spins slowly without spilling any water. This allows you to transfer all the water without any loss but it takes more time.

With a higher ISO, the waterwheel spins faster but spills a lot of water in the process. It takes less time but with big losses of water, or a loss in quality if you prefer.

What is the Best ISO for Digital Photography?

While the above information is useful in understanding what ISO is, the real question is what values you should use.

Unfortunately, it’s not as easy as saying that there’s one correct value that you should always use.

The general rule of thumb is that you want 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 your low ISO setting means that you need to use such a slow shutter speed that you no longer can get a sharp handheld image. My solution is then to either 1) increase the ISO until I reach a desired 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, or you’re photographing during nighttime.

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

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

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 be harmful to the image quality but there are many situations where you need to use one. I still recommend always using the lowest ISO you can get away with, even if that means a high value such as 6400.

Normally a high ISO is used for photographing:

  • In low light situations (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)
High ISO is important during night photography
High ISO is important during night photography

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

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. In most cases, you should use Base ISO for as long as possible.

Simply 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 wouldn’t be able to get sharp images with handheld. This is called long exposure photography.

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

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


I know that the ISO can be a very technical subject but I hope I was able to explain it in an understandable manner. 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 at first. With a little 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 gives 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 trying to keep your ISO as low as possible, regardless of what you are photographing. There is no reason to set it higher than needed.

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

Understanding ISO