What Does ISO Stand for in Photography? Understanding ISO for Beginners

In Photography Basics by Stefano Caioni Leave a Comment

ISO is difficult to understand and if you want to know more about it, you’ve come to the right place.

Understanding what ISO is as a beginner photographer, is key since it’s one of the most important camera settings. Together with aperture and shutter speed, it affects the exposure, and it can dramatically change the final look of your pictures. 

So, what does ISO mean and how to use it?

ISO determines how sensitive your camera sensor is to light. The darker the environment you’re shooting in, the higher the ISO needs to be to make sure you have the right exposure. ISO is one of the three main pillars of photography, and it’s part of the exposure triangle together with aperture and shutter speed.

But ISO also has the drawback of introducing digital noise (grain) into your images. We’ll see how this works in this article and how to avoid it.

What Does ISO Stand for in Photography?

ISO in Film Photography

ISO in Old Film Cameras

The International Organization for Standardization introduced ISO (also called ASA before) in old film cameras as a measurement of the film speed. The higher the “film speed”, the higher was the sensitivity of the film to light.

400 ASA film

ISO in Modern Cameras

In modern digital cameras, both DSLRs and mirrorless, ISO is an electronic emulation of the same effect. Instead of having to change film in your camera, you rotate a dial and select the different ISO numbers available to you. 

ISO is still today commonly referred by many as changing the sensitivity of your sensor, but technically this is not entirely correct.

Yes, ISO does affect the exposure triangle, allowing your camera to capture more or less light depending on its value. Still, it doesn’t mechanically change anything inside your camera

So what does ISO stand for in Photography?

Just for fun, let me try to give a more technical explanation of ISO.

Because of how a digital camera is structured internally, we can say that “ISO electronically amplifies the voltage observed at each pixel position before converting that voltage to a number. The effect of amplifying the gain of the photodetectors in the chip results in more grain in your image.”

It’s as if the light that hits the sensor is not pure light, but amplified light. This sounds way more complicated than it is and you shouldn’t bother too much about it. But let’s just accept that unlike aperture and shutter speed, ISO doesn’t “physically” change anything in your camera.

How ISO Works

ISO 200 on a camera

ISO is part of the exposure triangle, and it affects the brightness and darkness of your photos.

I want to make it really easy for you to understand this concept.

You can imagine that ISO is a setting that works on its own. Instead of working together with the other two elements of the exposure triangle (aperture and shutter speed), think ISO as an independent element of the exposure triangle.

This way, it’s simple to say that thanks to ISO, you can take photos in dark environments. If you are in a very dark environment, a high ISO value allows you to create a brighter image, without increasing the amount of light that hits the sensor. In contrast, with a low ISO value, you get a darker image.

ISO and the Exposure Triangle

To make sure we don’t oversimplify things, you must know what the exposure triangle is, and how ISO plays a part in it.

The Exposure Triangle

In photography, the exposure triangle represents the three elements of exposure and how increasing or decreasing one of them will require changing the other two to obtain a balanced exposure.

For this reason, you have to make sure you don’t rely only on ISO to balance your exposure.

Check also:

ISO and Image Quality (Noise)

Now that you know the meaning of ISO in photography, you have to learn how to use it to obtain great photos and improve the quality of your images.

You should rely on ISO when with the other two elements of the exposure triangle (aperture and shutter speed), you can’t achieve the exposure you want in your photograph.

In general, most people say that you should try to stick to the “base ISO” value to obtain the sharpest results.

That’s because high ISO values have the drawback of introducing digital noise (grain) in your images. Depending upon what camera you are using, the size and quality of the sensor, high ISO values can lead to a reduced quality of your image due to digital noise.

A few ways to reduce noise are:

  • Use a wider aperture and shoot at lower ISO
  • Use a slower shutter speed and shoot at lower ISO (might require a tripod)
  • Shoot in RAW. This allows you to capture more details in the scene and fix the image in Lightroom.
  • Use in-camera noise-reduction

Base ISO

The “Base ISO” or “Native ISO” is the unamplified sensitivity of the camera sensor. 

The base ISO of a camera is the lowest value available, and it represents the value with which you can obtain an image with the highest quality and the least amount of noise. 

The lower the ISO value you use, the better your image quality will be in terms of noise.

  • Most cameras offer a base ISO of 100.
  • Micro Four Thirds cameras (e.g. Olympus and Panasonic) offer base ISO 200. 
  • Cameras such as the Nikon D810 or the newest D850 go down to ISO 64.

Pay attention, your camera might have a setting called extended ISO.

If you are a beginner, I recommend avoiding it. But if you want to learn more about it, this video by Tony Northrup can clarify its usage.

What ISO Should You Use

Different environments, photography styles, and situations will require choosing a different ISO value.

Please note: consider the following as simplifications of possible ISO values. Each individual style of photography would require a more in-depth discussion to highlight all the aspects that contribute to delivering the right image quality.

ISO in Landscape Photography

At your camera’s base ISO value, you’re not adding any gain hence no noise. For this reason for landscape photography, you’ll need to shoot at your base ISO value whenever possible. 

Shooting during the golden hour, when the light is less intense, you might need to increase your ISO to 400 or even 800 if shooting handheld.

On a tripod, you can experiment with a long exposure technique and keep your ISO to 100 and slow down the shutter speed.

ISO in Nighttime Photography

If you’re shooting the night sky, you’ll need to use a really wide aperture. Since your image needs to be as sharp as possible, this is one of those cases where it’s easy to understand that you can’t rely only on ISO.

Increasing the ISO at its max will unnecessarily degrade your image, introducing noise. A long exposure is needed (slow shutter speed) to make sure your camera captures enough light without relying only on ISO.

Without going too much into the details of night sky photography, it’s enough to say that, in this scenario, you need to try and for example, start from an ISO value of 800

Depending on your camera, you will need to increase it until you see that the night sky is visible, and your photo is correctly exposed. 

Lastly, note that a full-frame camera will give you the best results introducing less noise at high ISO.

ISO in Portrait Photography

In portrait photography, you have to keep in mind that people constantly move, even slightly, when they are photographed. The facial expression changes, the posture and pose change as well, and this is especially true if you’re photographing kids.

For this reason, you need to use fast shutter speed to avoid introducing motion blur. Remember the exposure triangle described above. If you keep the aperture constant, the only way to get a fast shutter speed is to increase your ISO. Start from ISO 100, and depending on the light conditions, increase it to ISO 400 and check the results.

Darker conditions will require higher ISO or a proper light setting.

ISO in Street Photography

The ISO settings in street photography follow similar reasoning as portrait photography. To avoid motion blur, set your camera to aperture Priority, start from base ISO (100 or 200) and increase it as needed depending on the environment and light conditions. 

Usually, narrow streets are darker even during the day, start from ISO 400 in this case.

You can also break the rule, get creative, and use motion blur as a feature of your photo. To add this artistic touch, shoot in low light, and keep your ISO low. If you shoot in aperture priority, the camera will increase the shutter speed, introducing motion blur in moving subjects. 

ISO value for Wildlife Photography

As we’ve seen for street and portrait photography, your subjects will move. Animals are the most unpredictable and fascinating subjects.

To get the best light is often recommended to shoot during the golden hour, and some wild animals tend to show up right at that time of the day! As you now know, if you don’t want motion blur, you need to increase your ISO and use fast shutter speed.

Start from ISO 1000 and increase or decrease as needed. Always find the right balance between the noise introduced and the presence or not of motion blur.


Have fun experimenting with different ISO values on the field and see how the brightness of your image will change.

Make sure you keep the correct balance in your exposure triangle and ask your questions in the comments below if you need help understanding these concepts.

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