Guide to ISO in photography

Iso: How To Understand It (And Why It's Important)

Have you heard of ISO before? Is your head spinning yet? 

Would you prefer listen to the audio version of this article? Here you go:

First we covered aperture and shutter speed. And now get to speak about the third and last element of the exposure triangle: ISO

Let me ask you a question: 

Have you ever felt annoyed because all the photos of an important moment in your life came out all shaky? Like when your child was born, or when you tried to take pictures of your brother’s wedding? It’s pretty safe to say that this has happened to everyone. And it can be so FRUSTRATING (yes, I’m shouting).

Understanding these three concepts will make you more confident about your photography. And, as they say, you need to learn to walk before you can run. 

So let’s learn to walk!

What is ISO?

So what’s the use of ISO in photography, and how does it affect your photos?

ISO stands for International Standards Organization. It defined several standards for films and sensors in photography. In photography, ISO defines the sensitivity of film and it’s used in a similar way in digital sensors.

With a high ISO, you will be able to use a faster shutter speed. You might need this if you’re taking pictures in dark places like a candle-lit room or a street scene after dark.

What's The Drawback Of High ISO?

So what’s the drawback of a high ISO? At a high ISO, your pictures will have a tendency to show little spots, also called artifacts. Your pictures might start to look a little bit dirty. 


In film photography, we call these artifacts grain. You might also hear people speak about grainy pictures. In digital photos, we call these artifacts noise. 


Some people find the quality of the grain of certain films pleasing to the eye. In fact, you can buy presets to simulate these effects in your digital photos. This is quite subjective and will often be the source of heated discussions.


What's The Effect Of Different F-Stops?

So what’s the drawback of a high ISO? At a high ISO, your pictures will have a tendency to show little spots, also called artifacts. Your pictures might start to look a little bit dirty.

In film photography, we call these artifacts grain. You might also hear people speak about grainy pictures. In digital photos, we call these artifacts noise.

Some people find the quality of the grain of certain films pleasing to the eye. In fact, you can buy presets to simulate these effects in your digital photos. This is quite subjective and will often be the source of heated discussions.

Digital sensor have a fixed sensitivity

As you change the ISO in a digital camera, you’re not changing the sensor’s physical sensitivity.

What you’re doing in fact is adjusting the gain. This means that, depending on the ISO you entered, your camera adjusts the signal. With high ISO, it will amplify the signal more than with a lower ISO.

For non-technical people like me, this can be a bit confusing at the beginning. If that’s you, don’t worry about it. You don’t need to understand all the technical details to take great photos.

Let’s see what’s next.

ISO Numbers

Common ISO numbers are ISO 50, 100, 200, 400, 800, 1600, 3200, 6400, 12800 and 25600.

Notice how each full step from one ISO number to the next doubles or halves your exposure. Also, most modern cameras let you adjust the ISO in smaller increments.

In the end, the exact numbers you can dial in will depend on the exact camera you are using.

ASA Numbers

I noticed that a lot of people are taking an interest again in filmg photography. Before the introduction of ISO, photographers used to speak about ASA.

That’s why you might still hear some older photographers speak about “ASA 100” instead of “ISO 100”. At least I still heard people say that when I was growing up.

Me remembering this probably means that I’m getting old!

Film Photography And Noise

When I first started to take an interest in photography, digital cameras didn’t exist yet. We were quite restricted by the kind of film we could use, and ISO was a crucial element of film specifications.

With film, you haven’t got the same flexibility as with digital photography. With film photography, once you have chosen a film, you can’t change to a different film with a different ISO.

The only way to do that would be to use an interchangeable film holder. Or to fill up your current film first. With digital, changing the ISO is as simple as turning the settings wheel on your camera.

Beware that high-sensitivity films produce more artifacts compared to digital cameras. As time goes by, the difference between high ISO in film and digital will becomes more and more obvious.

I’m expecting that soon, we won’t need to worry too much about capturing artifacts in digital pictures.

What's The Best ISO?

Which ISO to use depends on what you’re trying to achieve. It’s like any other tool. You can’t say that one setting is better than the other.

Common Problems People Run Into

Some people might tell you that a low ISO is always better because of the lower noise or grain. But will you still believe them when all the photos you took at your sister’s wedding resulted in blurry shots?

In fact, I see that a lot of people are facing this issue. Either they keep using a low ISO without adapting to the lighting conditions.

Or they ignore the quality issues of high ISO completely. They’ll apply high noise reduction to their pictures. But then they’ll wonder why their photos look so unnatural.

I know what I’m talking about because I’ve done these errors myself. It’s so frustrating to mess up the pictures of a once-in-a-lifetime experience.

This has even led some people into legal trouble, and that’s a shame because it doesn’t have to be that way. There isn’t one best ISO setting, and you can’t apply a one-size-fits-all mentality.

Advantage Of Low ISO

Of course, it’s important to know that low ISO equals better image quality. With low ISO, there will be less noise or grain in your photos.

Not only that. Low ISO will benefit the dynamic range of your pictures. Dynamic range means how much detail your photos contains from very dark to very bright.

Also, your images will have richer colors with smoother transitions and less clipping. Color clipping works like exposure clipping. It means that your photo cannot capture a scenes full color details.

Base ISO

Each camera has got one ISO at which it will produce the pictures with the best possible image quality. Quite often, this will be ISO 100, but you’re best of researching the base ISO for the camera model that you’re using.

This is why many landscape photographers take their photos at ISO 100. 

When To Use A High ISO

But it’s also important to know that high ISO is your friend in low light situations where you cannot use a tripod.

This could be an event like a wedding or a family celebration which takes place indoors. Imagine if you tried to set up a big sturdy tripod in the middle of the living room.

The toddler would have a field day trying to knock it over. Your significant other would have a fit after walking into it with a plate of steaming potatoes!

So a high ISO will work better in these situations. Unless you’re trying to achieve some kind of creative effect, you’ll want family photos to be sharp. It sucks to find that the photos of your cherished memories are all blurry.

Sure, image stabilisation has come a long way, but there are still physical limitations to what you can do. Unless you’re a robot or a hybrid. Right now, these don’t exist yet. If they will in the future and you’re one of them, hello to the future! But I digress…

With some experience, you will identify the best ISO for different lighting conditions. And then you’ll be able to capture the type of look you’re trying to achieve.

Different Sensor Sizes

There’s something else you need to be aware of when you’re taking pictures with a digital camera. Every camera including mobile phones have got a smaller or bigger sensor.

You can use the different sensor sizes by using the crop factor. A micro four thirds camera has a crop factor of two compared to a full frame (also called 35mm) camera.

Cameras with bigger sensors also tend to be less sensitive to the issue of noise at high ISO settings. Mobile phones have very small sensors.

This explains why a lost of smartphones struggle in poor lighting conditions. The smartphones’ small sensors are a disadvantage compared to cameras with bigger sensor.

So remember: Smaller sensor = more noise // bigger sensor = less noise

Let’s now see which settings you should be aiming for in different situations.

Which Settings In Different Situations?

When should you use which ISO?

I’m going to simplify this a lot. Feel free to criticize me if you feel that this approach is wrong. If you’re getting started, don’t over-complicate things for yourself.

Start Here If You're A Beginner

If it’s too dark to maintain a low ISO and an acceptable shutter speed, raise your ISO settings. What’s an acceptable ISO setting?

A rule of thumb says that you should double your shutter speed compared to your focal length number.

Once you have a bit more experience, you can try the following techniques.

Special Lighting Situations

For landscape photos in the night, including stars or star trails, use a tripod. Then try using a low ISO setting and keep your shutter open for a long time.

Even during the day, if you want to take pictures with the best possible quality, try to use a low ISO. This is possible when your subject is not going to run away. For example landscapes, or flowers.

But with wildlife and sports, you’ll want to be able to take pictures with fast shutter speed in keep them sharp. That’s why you will have to raise your ISO more often than not.

How Do You Adjust The ISO?

So how can you adjust your camera’s ISO settings?

The way you adjust the ISO depends on the camera model you have. On a lot of cameras, you can use automatic ISO.

As you adjust your shutter speed and aperture settings, your camera will adjust the ISO.

What About Mobile Phone Cameras?

So how about mobile phone cameras? On most mobile phones, you can adjust the ISO. But be aware that, as mentioned earlier, smartphones have very small sensors.

This means that if you push your ISO too high, you will start to see excessive amounts of noise. So, before adjusting the ISO, ask yourself if there’s not another way to take the photo.

A lot of phones have got great stabilisation. I also like to lean my phone against a hard surface. You could also take a small bean bag or a mini tripod.


So what did we learn today? First, we discussed the basics of ISO and why it’s an important part of the exposure triangle. Then we looked into how you can use it in your photography.

I touched on the fact that there is not one best ISO and that you will need to adapt to the individual situation. Finally, we looked into the practical question of how you can adjust ISO on your devices.

Now you can go out and use your knowledge about ISO to create amazing pictures. Remember, this is like one big jigsaw. There’s no holy grail that will turn you into a master photographer.

Take your time, experiment and, most of all, enjoy yourself. This is not a competition after all, at least it shouldn’t be!

I hope you enjoyed this article and that you will apply your knowledge. The best thing you can do now is grab your camera and go outside (or stay indoors if you prefer).

Then, look at your images on a computer screen. Zoom in to see the effects of very high ISO and how clean low-ISO photos look.

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Thomas 😄

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How To Understand ISO In Photography