The Ultimate Guide to Camera ISO and Practical Tips

What is ISO on a Camera? Why does ISO matter? And most importantly, how does ISO affect your image quality? 

As an amateur photographer with five years of experience, I often get asked this from new photographers.

ISO is one of the easiest camera settings that every photographer needs to know. It plays a vital role in creating a quality image. 

In this post, you will learn what ISO is and how it affects your images. Plus, you will master ISO in digital photography.

camera iso setting
ISO value in photography simply explained

What is ISO?

ISO stands for International Organization for Standardization. For the purposes of photography, ISO refers to how much light enters your sensor and how bright or dark the image is. Just think of ISO as the camera’s sensitivity to light, and it would be fine. 

To make things easier, a high ISO makes your camera sensor more sensitive to light; therefore, the less light your camera sensor needs to make a well-exposed image.

You may ask what is a well-exposed image?

Generally speaking, a well-exposed image best reflects

  • the look
  • the feel
  • the mood

a photographer wants to express.

Conversely, a lower ISO makes your digital camera sensor less sensitive to light, so the more light it needs to make a correct exposure. 

Keep in mind ISO is one of the three main aspects of the exposure triangle; the other two are shutter speed and aperture.

These three most important camera settings work together to help you achieve a good exposure of an image.

ISO = Light Sensitivity of Cameras

How is ISO Measured?

ISO is measured in numbers – typical iso values are from 50 (low sensitivity to light), 100, 200, 400, 800 up to 10000 (very high sensitivity) – or even higher.

Every digital camera has a range of ISO values. The smaller the number, the less sensitive the camera is. ISO values double with each step of the range.

For example, an ISO value of 400 is double as sensitive as 200, which means the camera captures double light at ISO 400 than at ISO 200. Therefore, an image at ISO 400 will be twice brighter as ISO 200. 

How ISO Affects Image Quality and Noise

A good understanding of ISO helps you capture high-quality images in different lighting conditions, especially when dealing with low-light situations or dark environments.

Image noise or grain digital photography is a certain type of visual distortion, which is widespread, especially when shooting low-light photography. 

Increasing the ISO will also increase image noise:

When you increase ISO, more noise or grain will appear in your image, thus affecting its quality.

In reality, a noisy and blurry image can ruin all your special memories in the worst cases. For this reason, the general rule is to aim for the lowest ISO possible and avoid high ISO when you can.

High ISO Values = Image Noise

Noisy Image High ISO Clean Image Low ISO

The Difference Between ISO Sensitivity and Exposure

ISO sensitivity is simply how sensitive your camera is to light or how bright or dark the image is.

Exposure is the amount of light that reaches your camera’s sensor. Good exposure in photography generally combines the three legs of the exposure triangle – a proper ISO, shutter speed and aperture.

All three help you produce the effect that best matches your vision. 

What is Base ISO?

The base ISO is the lowest ISO number your camera can set to. It’s usually around 50 or 100. At base ISO, your camera produces the highest image quality without unwanted noise.

Base ISO = the Lowest ISO of Cameras

Although sticking to the base ISO, you can get the highest image quality. In many situations, maintaining your ISO at its lowest value (probably ISO 50 or 100) can be a challenge, especially in low-light conditions.

What is Auto ISO?

Your camera will “read” the light in Auto ISO modes and automatically choose a valid ISO value based on the scene’s brightness. Auto ISO is a handy feature for changing lighting conditions or when the subject is moving fast, so you don’t have time to adjust camera settings. 

For example, if you want to shoot a flying bird in shutter speed mode, Auto ISO works very well to help you freeze the bird’s movement. Auto ISO is very popular for most action photography, such as wildlife and sports.

However, suppose you’re shooting

  • landscapes
  • architecture
  • outdoor/indoor portraits, etc,

which usually don’t require high shutter speed.

In that case, Auto ISO is not recommended since it could pick a higher ISO than you need, producing unwanted digital noise for your image.

Camera auto ISO

How to Set the Right ISO in Camera

Photographers change ISO when they want to use specific values for aperture and shutter speed.

You can change ISO when your camera is in one of the following modes:

  • manual
  • program
  • shutter priority
  • or aperture priority

Although ISO setting varies from camera to camera, changing ISO is quite simple. Remember higher values provide greater sensitivity to light.

To set ISO, enter the camera’s menu and look for ISO sensitivity settings (Nikon), ISO speed settings (Canon), etc.

Take Sony A7III camera for example; there are four simple steps to change ISO:

  1. Open the menu1,
  2. Find the section of Camera Settings,
  3. Select “ISO Setting,”
  4. Choose the value to suit the brightness where you are shooting, or set it to Auto ISO, then it’s done.

Sony A7III iso menu

Most digital cameras as well as film cameras have a dedicated wheel or “ISO” button. It is worth being familiar with ISO settings since it impacts the darkness or light in your images.

What ISO Setting Should I Use?

What ISO number would be the best setting?

As a general rule, you want to set the lowest possible ISO(base ISO), as this will give you

  • sharp
  • clean,
  • and low-noise images

When to use low ISO:

On a bright and sunny day shooting with low ISO is easy as there is a lot of light to capture the image. So, a good starting point would be to set ISO at 50 or 100 if there’s plenty of light in the scene.

When to use high ISO:

Photographing in low-light situations such as

  • cloudy day
  • rainy day
  • overcast day
  • early morning
  • or nighttime walking

without a flash can be challenging.

A lower ISO setting can result in

  • dark
  • blurry
  • or grainy images

In that case, shooting with a higher ISO like ISO 800, and adjusting ISO according to the scene is best for shooting low light photography. Ensure to keep the correct balance in your exposure triangle. 

Best ISO for Outdoors

The key to a great outdoor image depends on how bright it is outside.

As a general rule, you will want to keep a low ISO — between 100 and 400 for crisp and grain-free results.

On a sunny and bright day, the ISO should stay at your camera’s base ISO, typically 50 or 100.

For cloudy days, you’ll have to choose a much higher setting – using between ISO 100 and ISO 400 gives you

  • sharp
  • clean
  • and well-exposed images

Best ISO Setting for Outdoors

Three People Hiking on High Mountain – ISO 100

Photographing the outdoors such as

  • national parks
  • caves
  • wildlife
  • nature, etc.

is enjoyable but requires practice and patience.

You will use natural light and a narrow aperture like f/8 and create a large depth of field (so you can get as much as possible in focus).

Best ISO for Night Photography

Things look more interesting but very different at night; you will likely adjust ISO quite often, especially if you shoot in low light conditions.

Therefore, you need to make some compromises – use a higher ISO to allow enough light to reach camera sensor, and get a properly exposed image in the dark.

While the exact setting varies from one shot to another, in most circumstances, between ISO 1600 and ISO 6400 is great for night shooting so your camera has “acceptable” noise.

However, most modern cameras take a nice clean image at ISO 3200.

Best ISO Setting for Night Photography

Back View of a Woman Walking on Street at Night – ISO 3200

Shooting night photography (city scenes like streets, bridges and buildings, lightning, starry sky, moon, etc.) can be fun, exciting, and challenging for beginners. To capture beautiful images at night, besides high ISO, wide-angle lenses with a fast aperture and slow shutter speed are highly recommended for capturing night scenes.

Best ISO for Astrophotography

Using ISO 800 for a 30-second exposure is a great starting point. Then increase the ISO when there is not enough light that enters the camera.

Take some test shots, check your exposure, and get your histogram dialed in.

Whether you feel comfortable or not depends on if there is any light pollution and your personal preference. 

Best ISO Setting for Astrophotography

Teepee Under A Starry Sky – ISO 800

Shooting astrophotography can be fun but also daunting. If you’re a beginner to this hobby, besides high ISO, use

  • widest possible lens
  • a fast aperture
  • and shutter speed in the 20-30 second range

if you want a colorful, sharp landscape Milky Way image.

Best ISO for Outdoor Portraits

You want the ISO to be as low as possible for sharp and clean images. A setting between ISO 100 and ISO 400 would be best in many circumstances. Even so, it’s best to test it out for yourself to be sure. 

Best ISO Setting for Outdoor Portraits

Girl in Floral Dress Posing in a Wheat Field – ISO 100

Outdoor portrait photography mostly in

  • local parks
  • lakes
  • beaches
  • downtown streets
  • local coffee shops, etc.

is fun and a vital photography technique to master.

Besides low ISO, beginner portrait photographers should use natural light, along with a wide aperture like f/1.2 or f/2.8 to blur out the background, and a low shutter speed like 100 or 200 if your subject will be standing still.

Best ISO for Indoor Portraits

ISO 100 or 200 works very well if you are on a tripod when shooting inside.

If hand-holding without a tripod, you have to boost it up to 800 or even 1000 to avoid camera shake.

Best ISO Setting for Indoor Portraits

Female Meditating Indoor Portrait – ISO 100

Shooting indoor portraits such as


hotel lobbies,

flower shops,



botanical gardens, etc.

can be exciting and challenging.

Besides ISO, a wide aperture like f/4 or less, and a fast shutter speed like 1/100 or a slower shutter speed If you are on a tripod are highly recommended for clean, crisp images.

Best ISO for Landscape Photography

Use the lowest possible ISO or base ISO for landscape photography, since detail can always be teased out of shadow areas in post-processing if shooting at ISO 100 or 200.

Best ISO setting for Landscape Photography

Autumn Nature Landscape – ISO 100

Landscape photography like shooting

  • mountains
  • running water
  • the sea/coastal areas, etc.

is very appealing. There are many unique places with varied landscapes for you to explore and photograph.

For beginner photographers, besides low ISO, a slow shutter speed like 1 second to capture motion or a fast shutter speed like 1/500s to freeze motion, and a narrow aperture like f/16 for a deep depth of field to keep everything in focus is highly recommended. 


ISO is an important subject to understand for photographers who want to improve the quality of images.

The general rule is to shoot with a low ISO value as much as possible and avoid high ISO.

In reality,

  • light
  • along with shadow
  • colors
  • and other elements

changes throughout different times of the day.

Just remember, practice makes perfect. You’ll see how easy it is to master the ISO and select your preferred settings with enough practice.

This introduction to ISO should hopefully get you started with the concept of ISO.

By mastering the ISO in every situation, you’ll take a big step towards creating more successful images.

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