What Is Camera ISO And How To Use It In Your Photography

ISO is part of the exposure triangle (Shutter Speed, Aperture, ISO) which you should understand in order to get the most out of your camera.

ISO not only influences the exposure of your image, but it also has an impact on image quality.

In this article, we attempt to explain ISO in simple terms and show how it works in practice.

What Is ISO?

ISO speed measures how sensitive your image sensor (digital camera) or film (film cameras) to light.  

  • Lower ISO values mean your sensor is less sensitive to light.
  • Higher ISO numbers indicate the opposite, increased sensitivity to light.

On digital cameras, the ISO scale normally starts at 100. From there it doubles continuously until you reach the limits of your camera.

For example: 100 > 200 > 400 > 800 > 1600 > 3200.

However, many digital cameras will allow you additional ISO stops by allowing you to set your camera at 1/3-stop intervals. That’s why you’ll often see numbers like 125, 160, 240, 320, 640, and so on in your ISO settings.

How Does ISO Affect Exposure?

Since ISO is a measure of how sensitive your image sensor to light, a higher ISO means a brighter image. A lower ISO means a reduced exposure/brightness.

Take a look at the six example images above. All of the photos were shot using the same shutter speed (1/15 sec) and aperture (f/2). The only setting that was changed is the ISO, which I doubled for each new exposure. As you can see, by doubling the ISO, I made each image twice as bright as the image before it.

A series of images showing the effect of increasing ISO on photo's exposure
As we increase ISO speed, the photo becomes brighter/more-exposed

ISO and Image Noise

Image Noise refers to the grainy spots or distorted pixels in a photograph which lowers its image quality. One of the reasons for image noise is high ISO. At around ISO 400-800 you may first notice noise appearing in the flat areas of the image. As your ISO increases to 1600 or more, the noise will become notably visible throughout the whole image.

Keep in mind not all cameras handle ISO-induced noise the same way. Usually, cameras with small sensors, like smartphones, start to show heavy noise even at low ISO numbers. Generally speaking, the bigger the sensor, the better the camera will handle noise. The images of the Hasselblad shown in the previous section are shot with a Canon 5D Mark iii equipped with a full frame sensor. However, the small preview size means you won’t even notice the noise at ISO 6400. Read this wiki for more info on image noise.

Let’s Take A Closer Look at ISO Induced Noise

Let me illustrate the ISO speed’s noise effect by these four large photos of a plant I photographed in my garden. Again, the images are all the same composition. The only difference is the ISO they were shot at.

A sample image at iso 100
ISO 100 is The lowest ISO value I can choose on my Canon 5D iii. As you can see, the image quality is crisp and clear and grain is practically not visible.
A sample image at iso 800
My full frame camera handles noise so well, even at ISO 800, grain almost stays invisible. Nevertheless, if you look closely in the out of focus areas, it starts to appear in the shadows (dark-green areas).
A sample image at iso 6400
Compared to ISO 800 the noise at ISO 6400 is much more visible. When searching your photos for noise, it’s best to look in flat, out of focus areas. The structure of the leaf in focus hides the grain pretty well.
A sample image at iso 25600
The noise is very noticeable at ISO 25600.

Despite the visibility of noise, there is another unpleasant effect you can observe at ISO 25600. Look closely at the brightest part of the leaf. The higher the ISO goes, the brighter this part gets. In fact, it just turns white and the texture of the leaf gets lost. Be aware! High ISO values have a negative effect on how your camera handles the very dark and very bright parts of your image.

Noise reduction options:

One last thing I should mention before we move on, modern DSLRs offer built-in noise reduction options. But I don’t recommend you activate them. They only smooth out the noise. Your image will look flat and fake, almost as if you airbrushed it. Post-processing software has come a long way. I suggest you handle de-noising on the editing end of things using a post-production software such as Lightroom or Photoshop.

Related Article: Lightroom Tutorials

ISO Performance of Your Camera

As all digital cameras differ from each other in the way they handle noise, it’s somewhat relative what a low ISO is. Before owning a full-frame camera I owned a camera with an APS-C sensor. It was a very decent camera that took nice pictures. Nevertheless, I tried to avoid shooting with an ISO higher than 1600 as the noise started to get really heavy. With my full frame camera, I wouldn’t have a problem shooting in ISO 6400.

I recommend you test your camera’s ISO performance by taking a series of photos at different ISO settings like I’ve done above. Then give the images a closer look on a bigger screen and decide what is acceptable for you. It’s always useful to know your camera’s capabilities and limitations. It will help you make smart decisions when you’re out shooting.

Avoid Auto ISO

You should always set up your ISO the way you need it for certain situations. Let’s assume you are capturing your little brother’s birthday party. Because he is much younger than you and his guests can’t sit still for longer than a few seconds at a time, a lot of movement is going on. What if you want to freeze the action? In order to freeze action, you need shutter speeds of at least 1/125, if not 1/250.

With that in mind, if the party happens to be outside in the garden on a sunny day, you probably won’t have any troubleshooting at an ISO in between 100-400. However, if you’ll be shooting inside, things can get trickier. In order to achieve such shutter speeds in dimmed light, you often need higher ISO values (more sensitivity to light). You may need to push the ISO up to 1600, sometimes even 3200. This will help you shoot with quicker shutter speed, allowing you to freeze the action.

Set a Limit for Auto ISO

If you would still like to use Auto ISO setting of your camera, we recommend that you set an upper limit. You should set this to the maximum ISO level at which your camera can still produce an acceptable image quality.

camera menu screenshot for setting auto ISO upper limit
If you are using auto ISO, it is a good idea to set an upper limit

Use the following ISO settings as a starting point next time you’re out practicing. Take several test shots at different ISOs and find the best exposure. Here are some ISO guidelines for different situations.

  • 100-400: Outside during daylight.
  • 400-1600: Inside and outside during twilight or cloudy days.
  • 1600-higher: Any low light situation.

Of course, these are only general guidelines. There are a lot of variables that go into determining the correct exposure–we’ll be covering those later on! Just keep in mind, experimenting with different settings is a great way to supplement what you’re learning here.

For street photography, I set my camera to ISO 400 at least 80% of the time. Even when it’s bright enough out where I could shoot with ISO 100, I personally leave it on ISO 400. During the day, ISO 400 works perfectly for almost all the situations I encounter on my walks. More importantly, it allows me to close down the aperture more, giving my photos more depth of field and sharpness.

However, when I’m passing through shopping malls and areas with heavy shadows, my ISO ranges in between 400 and 1600. Though I must admit, I rarely use ISO values higher than 1600.

Take Away

Higher ISO’s allow you shorter exposure times, but keep in mind, the sacrifice of a high ISO setting is the loss of image quality. In practice, ISO is the first setting I adjust. I quickly choose my ISO before I start walking and I don’t think about it until the light changes and I can no longer shoot at my desired aperture without increasing the ISO.

If you have any questions about ISO and its effect on your photos, I am glad to answer you in the comment section below. Happy shooting!

Download FREE Photography Lighting Cheat Sheet

Subscribe and get a free downloadable photography lighting cheat sheet

Thank you for subscribing.

Something went wrong.

learn camera iso cover photo

About the author

Ramesh Yahathugoda

My love for photography started when I went on a hiking trip to Alberta's Banff national park. I have more than 10 years of experience shooting nature and landscape photography and I am a member of Professional Photographers of Canada (PPOC).

My passion is to help others become better photographers. I share photography knowledge and review camera gear on PhotoBlog's official blog to achieve that goal. In my spare time, I love to read, run, and go on hikes! To see my latest adventures, visit my travel photography blog here on PhotoBlog.com

Send this to a friend