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What is ISO? A Simple Explanation With 10 Real-World Examples

by Tom Shu

Last Updated on November 9, 2020 by Tom Shu

As Albert Einstein once said, “if you can’t explain it simply, then you don’t understand it.” So, in this article, my goal is to explain ISO in as simple a manner as I can.

I’m not going to get into any technicalities or specifics about what ISO is as there are many other resources out there. However, what you will find in this article is a no-fluff explanation of how ISO impacts you as a photographer, plus 10 of my own examples showing how ISO works in the field.

Overall, what’s important to understand is that ISO is just one of the levers you can pull to help you when capturing photos. You don’t necessarily need to understand it deeply, you just need a good enough understanding in case you find yourself in situations where it’s best to adjust your ISO manually or let the camera decide on automatic ISO.

So, What is ISO?

Put simply, ISO is a way for you to adjust how bright or dark your photo is with all other settings being equal. Since ISO can brighten or darken an image, it will give you more flexibility in using the shutter speed and aperture that you want for the image.

Let’s use this photo as an example where increasing my ISO gave me the flexibility to shoot at a higher shutter speed than I normally would have been able to in this dark environment. 

girl in yellow dress and blue scarf in a forest

In this scenario, I was taking a series of photos of Melissa in the Hoh Rainforest on a cloudy day, so it was pretty dark. The main goal for the photo was to add a bit of whimsy to the image by capturing her twirling dress amidst the lush forest. 

To freeze the movement of her dress I used a shutter speed of 1/250 and for aperture, I used f/2.8 as that is the fastest aperture on my lens. 

Since the aperture and shutter speed were locked, the only variable I could change at this point was ISO.

I ended up cranking my ISO up to 1250 to capture the image. In this situation, changing the ISO allowed me to use a shutter speed fast enough to freeze her movement while keeping the image properly exposed. 

Notes From The Field: Increasing your ISO too high will introduce noise into your photo. However, what’s important to understand is that every camera handles higher ISOs differently, so it’s important to understand how your camera handles ISO.

What to Consider When Picking Your ISO?

illustration of different things to consider when using ISO

Yes, understanding ISO is important, but In reality, because of how advanced camera technology is now, you don’t need an incredibly deep knowledge of ISO to use it appropriately in the field. 

If you have a mirrorless camera, one of the easiest ways to learn how to use ISO manually when taking photos is to change your ISO as your composing your image. With mirrorless cameras, you’re able to see a live preview of what your image will look like with all the settings you have selected. The camera should also be able to tell you if you’ve exposed the image properly.

Over time as you shoot in a variety of different situations, you’ll get a better understanding of what ISO works best for the image you’re trying to create in the environment you’re in.

From a realistic perspective, here are the most important  things to consider when you’re changing ISO for your photos:

Every Camera Handles ISO Differently

illustration of hands holding camera

As I mentioned, one of the first things you should do is to figure out what the maximum usable ISO is with your camera. Once you have the maximum ISO figured out, it’ll make it much easier to adjust your ISO without worrying about introducing too much noise.

For example, I’ve found the maximum usable ISO that I’m comfortable with using with my Sony a7R III to be ISO 5000. In most cases, any photo taken under ISO 5000 will be usable. Now, this is not to say, these photos shot at ISO 5000 are the best quality and won’t have noise, but they’re still usable.

What are You Taking the Photos For?

gif of girl holding up a camera

Casual Photos: I think your thought process about ISO can be a little different if you’re just taking photos to share with family and friends on social media. For these photos, don’t be afraid to push the maximum usable ISO limits of your camera if have to as it won’t be as big of a deal if you introduce noise into your photos. Unless you’re pushing your camera way past its usable range, it’s most likely that your friends and family will not notice if your photo is noisy or not.

Professional Photos or Client Work: On the other hand, if you’re taking photos professionally, it’s important to keep your ISO under your camera’s maximum usable limit and. Preferably, depending on the environment you’re shooting in, you want to keep ISO as low as possible to get the cleanest image possible. With that said, I have submitted photos to several clients that were shot at high ISOs (>1000) which they were happy with.

Don’t Be Afraid to Use High ISOs

illustration of iso setting

Don’t be afraid to shoot at high ISOs when you need it. One misleading statement that I have heard over and over again is to “keep your ISO as low as possible”. This is misleading because each situation you’ll be shooting in is different and the only option you may have is to use a high ISO. 

A better way to rephrase this statement is that you should keep your ISO as low as the shutter speed and aperture you’re using allows

To get a better idea of why you shouldn’t be afraid use high ISOs, take a look at the 10 example photos below. All of these photos were delivered to clients and many were taken at high ISOs above 1000.

When to Use Auto ISO Versus Manual ISO

illustration of automatic setting on camera

Don’t just think that the automatic ISO setting on your camera is only for amateur and beginner photographers. Many professional photographers including well-known legendary photographers like Jimmy Chin use auto ISO and the camera’s automatic modes depending on the situation they’re shooting in.

What’s important for you to understand is when it might be best to use Auto ISO vs going full manual ISO.

Based on my own experiences, here is when I think it’s best to utilize your camera’s Auto ISO vs setting the ISO manually.

Auto ISO

  • If you’re shooting in varying light conditions and you need to quickly capture the shot. This could be in sports photography, wildlife photography, or even wedding photography.
  • If you’re shooting in aperture priority mode and have set a minimum shutter speed (more on this in the “Notes From The Field” below).
  • Any time you want to go full automatic whether that’s in auto mode, shutter speed priority, or aperture priority.
  • If you’re quickly moving between different settings. 

Manual ISO

  • When you’re shooting in a high dynamic range situation (such as sunrise, sunset, portrait photography) and there is a big difference between the brightest and darkest parts of the photo. 
  • Low light situations when you can use a slow shutter speed to capture more light and can stabilize your camera. Examples of these situations might include landscape photography or interior architecture or photography. 
  • If you have time to set up for your shot. 
  • Any time you’re shooting under artificial lighting (also good to manually set white balance too).

Notes From The Field: One of the best ways to use auto ISO with aperture priority is to set a minimum shutter speed. This will ensure your shutter speed is fast enough to capture the action without motion blur while allowing you to use the aperture you want.

10 Real-World Examples of Using ISO

gif illustration of the world bouncing up and down

Instead of just talking about ISO, let me show you how I’ve used ISO to make a variety of different photos. Most importantly, notice how well modern cameras perform at high ISOs above 1000 and even up to 4000.

In these examples, my goal is to walk you through my thought process, what aperture and shutter speed I used, and how and why I chose the ISO for the image.

Example 1 – Starry Night

image of night sky with stars over a lake

PHOTO SETTINGS

  • Camera: Sony a7R III
  • Tripod: Yes
  • Focal Length: 24mm
  • Aperture: f/2.8
  • Shutter Speed: 25 seconds
  • ISO: 1600

This astrophotography photo was taken at Kachess Lake in Washington State. As with any astrophotography photo, I had to use a tripod to stabilize the camera to use a longer shutter speed to capture the stars. 

The 25-second shutter speed I chose to use for the photo was important for two main reasons. 

1.) Most importantly, I didn’t want to capture any star movement. For the wide-angle focal length of 24mm, 25 seconds was the maximum shutter speed I could use before motion blur from the stars would be introduced into the image (see Field Notes below for more info).

2.) It allowed me to keep the ISO at 1600, which is well below ISO 5000, which is what I consider the maximum usable ISO for the camera.

I think this photo is a great example of what cameras can do when you can stabilize and use longer shutter speeds. Even though there was only a sliver of available light from the stars and the city in the distance, I was able to use just a medium/high ISO of 1600 to produce a very clean image with minimal noise.

Notes From The Field: In case you’re wondering, I used the 500 Rule to calculate what shutter speed I should use for this image. The 500 rule states that if you don’t want to capture star trails (movement of the stars) then you should divide 500 by the focal length you’re using to calculate the shutter speed. So if you’re using a 24mm focal length, then the maximum shutter speed you could use before star trails appear is 21 seconds (500 ÷ 24mm focal length = 21-second maximum shutter speed).

Example 2 – Sushi Jumping

image of dog running through the grass

PHOTO SETTINGS

  • Camera: Sony a7R III
  • Tripod: No
  • Focal Length: 70mm
  • Aperture: f/4
  • Shutter Speed: 1/1000
  • ISO: 3200

This photo was taken of Sushi at a park right after sunset. It was a tricky image to capture for the following reasons:

  1. There wasn’t a lot of light to work with.
  2. I needed to use a fast enough shutter speed to freeze Sushi while she was running
  3. I needed to use a narrow enough aperture to make it easy to focus as the Sony a7R III’s screen was difficult to use at this angle.

I tried out multiple combinations of aperture and shutter speed. 

For aperture, I found that f/4 worked best. The f/4 aperture was shallow enough to throw out the background at 70mm, but at the same time, it was narrow enough to make it easier to hit focus. 

On the shutter speed side, 1/1000 was fast enough to freeze Sushi, while being slow enough to allow me to keep the ISO at a reasonable level.

Since the aperture and shutter speed was locked in, the only variable I could realistically change to brighten up the image was ISO. The ISO of 3200 I used was higher than I initially wanted it to be, but it was still well within the ISO range to produce a clean image with very minimal noise.

Example 3 – Winter Wonderland

image of snow covered scene with house and lights that look like stars

PHOTO SETTINGS

  • Camera: Sony a7R III
  • Tripod: No
  • Aperture: f/2.8
  • Focal Length: 24mm
  • Shutter Speed: 1/40
  • ISO: 2500

This photo was taken at the top of Grouse Mountain during their Peak of Christmas holiday event. What made this photo more difficult to capture was that there was not much light to work with and I didn’t have an option to stabilize the camera. 

Luckily, the composition worked well with a wide-angle focal length of 24mm so I had some flexibility in keeping the camera stable while using a slower shutter speed. (see the Field Notes below for some guidance on how to pick a shutter speed based on the focal length you’re using).

I found the slowest shutter speed I could use while keeping the photo sharp was 1/40. This meant that I had to increase my ISO to 2500 for the image to be properly exposed.

Similar to the above two photos which were shot at ISOs above ISO 1000, notice how clean of an image I was able to create even at these high ISOs.

Notes From The Field: If you’re ever in a situation when you’re not sure what shutter speed to use to keep your image sharp without a tripod, a good rule of thumb is to use a shutter speed that is equal to or greater than the focal length you’re using.

Example 4 – Capilano Suspension Bridge

image of a suspension bridge with lights on both sides

PHOTO SETTINGS

  • Camera: Sony a7R III
  • Tripod: No
  • Aperture: f/4.0
  • Focal Length: 37mm
  • Shutter Speed: 1/160
  • ISO: 500

This photo was taken on Capilano Suspension Bridge in the middle of December on a very rainy day. It was a pretty simple shot to execute because I only had to focus on center framing the bridge and didn’t have any other subjects in the composition. The only variable that made the photo more complicated was the movement from the suspension bridge. Additionally, because I had the flexibility to do so, I wanted to keep the ISO as low as I could, which ended up being ISO 500.

To counteract the movement from the bridge, I chose a shutter speed of 1/160. This was fast enough to prevent any motion blur and was slow enough to allow enough light in.

Then for aperture, I chose to use f/4.0. This allowed me to keep the entire image sharp and at the same time, it allowed the most light into the image which gave me the flexibility to keep a lower ISO at 500.

Example 5 – Magic Second Beach

image of a girl in yellow dress twirling on a beach

PHOTO SETTINGS

  • Camera: Sony a7R III
  • Tripod: No
  • Aperture: f/5.6
  • Focal Length: 34mm
  • Shutter Speed: 1/250
  • ISO: 64

This photo was taken at Second Beach in Olympic National Park on a sunny fall afternoon. My three main points of focus in this image were to:

  1. Use a shutter speed fast to freeze Melissa’s dress while she twirled without any motion blur.
  2. Choose a narrower aperture to prevent the sea stack from being thrown completely out of focus. Note: I needed to keep this in mind as there was a significant distance between Melissa and the sea stack.
  3. Center frame both Melissa and the sea stack.

Even with so many variables, what made this photo easier to execute was that it was so sunny out. Since there was so much light, I didn’t have to worry about underexposing the image, so I just used the lowest ISO setting on the camera which is ISO 64.

Example 6 – Rialto Beach at Sunset

image of the ocean with seastack in the background with sunset sky

PHOTO SETTINGS

  • Camera: Sony a7R III
  • Tripod: No
  • Aperture: f/5.0
  • Focal Length: 200mm
  • Shutter Speed: 1/200
  • ISO: 800

This photo was shot at Rialto Beach at sunset. It was one of the more memorable photos I’ve created because of the different natural variables I was working with.

My three main goals with this photo were:

  1. Compress the sea stack and the ocean waves as much as I could to make them appear larger than life in the image.
  2. Keep the sea stack in focus while blurring out some of the ocean waves in the foreground to create depth of field and frame the image.
  3. Properly expose the sky so I could accentuate the sunset colors.

The most important aspect of executing this photo was to use a focal length of 200mm to compress the image as much as I could so aperture and shutter speed was selected to support this. 

First, I chose a shutter speed of 1/200 (which is equivalent to the focal length) to make sure there wasn’t any motion blur from camera shake or the ocean waves. For aperture, I chose f/5.0 to keep the sea stack sharp while being wide enough to blur out some of the foreground for additional depth of field.

On the ISO side, the sunset sky was still decently bright, so I only had to increase to ISO 800. This was the maximum ISO I could use before blowing out the highlights in the sky.

Notes From The Field: Because of the dynamic range in this image, I purposefully underexposed the foreground to prevent blowing out the highlights. I then brightened the foreground and shadows in post-processing using Lightroom.

Example 7 – Robot Restaurant Show

image of a drummer during a show

PHOTO SETTINGS

  • Camera: Sony a7R III
  • Tripod: No
  • Aperture: f/2.8
  • Focal Length: 47mm
  • Shutter Speed: 1/1250
  • ISO: 4000

This photo was taken at the Robot Restaurant Show in Tokyo. It was very difficult to take photos during the show because of how dark the environment was and how quickly the performers were moving. 

To give me a chance of capturing usable images, I knew I had to use a fast shutter in combination with a high ISO. After testing a variety of different settings, I found the combination of a shutter speed of 1/1250 and an ISO of 4000 to work the best. 

One positive which made it easier to take photos was that the lighting condition didn’t change much. So, once I got my settings locked in, I didn’t have to worry about changing them and just had to worry about composing the shot. 

What surprised me the most was just how well the camera performed at ISO 4000 in this environment.

Example 8 – Mount Fuji Pirate Ship

image of a pirate ship on lake in front of mount fuji

PHOTO SETTINGS

  • Camera: Sony a7R III
  • Tripod: No
  • Aperture: f/5.0
  • Focal Length: 196mm
  • Shutter Speed: 1/250
  • ISO: 1000

This photo was taken at Lake Ashi in Hakone, Japan as we waited to board the pirate ship to take us across the lake. My main focus in this image was to use a telephoto lens (used 196mm) to compress Mount Fuji in the background so it could loom large over the pirate ship.

At the same time, I didn’t have a tripod so I needed to use a fast enough shutter speed (shutter speed of 1/250) to prevent motion blur from the moving ship and any minor camera shakes.

It was nearing sunset and the clouds were just clearing up from a full day of rain so the lighting condition was gray and dreary. Because of this, I had to increase ISO to ISO 1000 to properly expose the image with the setting combo of f/5.0 and shutter speed of 1/250. 

I could have also dropped my aperture to f/4.0 which would have allowed me to decrease the ISO, but I ended up choosing  f/5.0 to keep Mount Fuji more in focus as the focus point was on the pirate ship.

Example 9 – Mount Fuji in the Clouds

image of mount fuji rising above the clouds with sunset colors

PHOTO SETTINGS

  • Camera: Sony a7R III
  • Tripod: No
  • Aperture: f/4.0
  • Focal Length: 158mm
  • Shutter Speed: 1/125
  • ISO: 4000

This photo was taken while riding the Hakone Ropeway during sunset. The cool thing that happened on this day was that right at sunset, the clouds cleared up so we could see Mount Fuji above the clouds with the sunset colors lighting up the sky.

Overall this was a very difficult image to capture for the following reasons:

  1. There was little to no light to work with.
  2. I wanted to use a telephoto lens to “enlarge” the size of Mount Fuji and my telephoto lens has a maximum aperture of f/4.0
  3. I was in a moving gondola so had to use a fast enough shutter speed to prevent motion blur.

In the end, the most optimal settings I found for this photo were an aperture of f/4.0, a shutter speed of 1/125, and ISO 4000. I also tried to shoot this image above ISO 5000, but the images were way too noisy to use.

I think this photo is a great example of doing the best that you can with the situation you’re given. Yes, I wish I could have produced a cleaner image with less noise, but given the situation, it was the best I could do. I’m just glad I was able to capture a somewhat usable image versus no image at all.

Example 10 – Blue Hour in Mount Rainier National Park

image of girl standing on a log in front of a river and mountains in the background

PHOTO SETTINGS

  • Camera: Sony a7R III
  • Tripod: Yes
  • Aperture: f/8.0
  • Focal Length: 108mm
  • Shutter Speed: 2 second
  • ISO: 64

This photo was taken in Mount Rainier National Park during blue hour. The reason why I wanted to include this image is to show you how big of a difference a tripod can make when talking about ISO.

For this image, I used an aperture of f/8.0 and a focal length of 108mm as I wanted to compress the river and mountains in the background while keeping the entire image sharp. Because of the limited light available during blue hour, there would’ve been no way I could have achieved this look without a tripod.

Since I had a tripod to stabilize the camera, I was able to use a 2-second shutter speed to keep the ISO at its lowest rating of ISO 64.

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