The Highs and Lows of ISO and How to Use it to Your Best Advantage

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Treating ISO as the foundation of the exposure triangle and only adjusting it when you really need to will help you produce more consistently creative photographs.

Asian woman taking a photo - all about ISO

ISO 100 (allowing a wide aperture setting).

ISO stands for International Standards Organization, which does not really help you understand what it is. But it does indicate the standard is international and it is constant across all brands and types of cameras.

The ISO is the measurement of how responsive your camera’s sensor is to light. The lower the numeric value, the less responsive, the higher the value, the more responsive.

Editor’s note: ISO is actually much more complicated than that but for purposes of this article, this is generally considered the easiest explanation of ISO to understand, especially for beginners. 

Close up of twp people holding DSLR cameras - ISO settings

ISO 400

Low ISO

Choosing a low ISO setting, say less than 400, is best when there’s a lot of light or when you have a tripod and the style of photograph you want to make allows you to use a long exposure. When the ISO setting is low, the sensor is less responsive to light, so, therefore, it requires more light to create a well-exposed photograph.

Using a low ISO setting will result in better technical quality photos generally. There will be little or no digital noise, the colors and contrast in your images will be better.

Woman standing in a fresh market holding vegetables - ISO 100

ISO 100 allowing for a slow shutter speed in bright light. My friend was standing very still and my camera was on a tripod.

High ISO

Choosing a higher ISO setting is best when the light is low or you are not able to make a long exposure. Higher ISO setting means your camera’s sensor is more responsive to light, so it needs less light to reach the sensor to create a well-exposed photograph.

It also means the technical quality of your images may be affected by digital noise, colors may be less vibrant and overall image contrast is flatter. How much, depends on how high you have your ISO setting and your camera model.

Sensor technology is rapidly changing and, if you have a newer, higher-end model of camera you can more confidently choose to make photos at higher ISO settings than with older, lower-quality cameras.

Sky lanterns being released in Chiang Mai during Yee Ping festival - high ISO

ISO 6400. Allowing a fast enough shutter speed to avoid motion blur in the lantern in low lighting conditions.

When and Why to Adjust the ISO

Unlike shutter speed and aperture settings, the ISO setting has no direct creative impact on your photographs. If you think the inclusion of obvious digital noise in an image mimics a creative value similar to film grain I suggest you do some more serious study on the matter.

Adjusting the ISO can assist you to achieve the shutter speed and/or aperture settings you desire to create the style of photograph you have in mind.

Street scene at night in Thailand - ISO

ISO 100 allowing a very slow shutter speed (long exposure).

ISO and Aperture Creativity

If you are wanting to blur a background using a wide aperture setting when the light is bright, you will need to adjust your ISO to one of the lowest settings to accomplish this. If you were to use a high ISO setting you may not be able to obtain a good exposure with a wide enough aperture setting, so your background will not be as soft looking as you want it to be.

Asian woman portrait - ISO

ISO 160 allowing a wide aperture setting to achieve a blurred background.

Alternatively, if you want to create an image where everything in your composition is in sharp focus, it is best to choose a higher ISO, especially when the light is not so bright. By choosing a higher ISO you will be able to set your aperture to a higher f-stop number and achieve a greater depth of field than if your camera were set to a lower ISO value.

ISO and Shutter Speed Creativity

Choosing a low ISO can assist you in achieving a slow shutter speed when you want to create a photograph incorporating some motion blur. If you are photographing a moving subject, like a waterfall, and wish capture a lovely silky effect in the water, you will need to use a slow shutter speed.

This is easier to do when your ISO setting is low.

Mae Ya Waterfall - low ISO

ISO 50 on a bright day to set the shutter speed slow enough to capture motion blur in the water.

Freezing action by using a fast shutter speed will often require you to choose a higher ISO setting, especially if the light is not so bright. Being able to adjust your shutter speed so that is will render a fast moving subject as though it’s frozen in time will often mean balancing your exposure with a higher ISO.

Auto ISO

If you are comfortable with having your camera in control of your exposure, then Auto ISO is a good option to consider. If you set your ISO to Auto as you adjust your aperture and/or shutter speed settings, the ISO will modify itself to make an exposure the camera finds appropriate.

Night time photo of Chedi Luang Thailand - ISO 800

ISO 800

If you do choose to work with Auto ISO, I recommend you do some testing first to discover what maximum ISO setting you are comfortable with for your camera.

To do this, take a series of photos of the same subject in the same lighting conditions and double your ISO setting each time. Then compare all the photos (look at them close-up and full image) and find the ISO setting for the image you are comfortable with, the one just before you see too much digital noise.

Editor’s note: Try not to overly pixel-peep. By looking at your images at 100% on your computer screen you will not get a true feeling for the amount of noise which will be visible at a normal viewing distance. 

Many cameras have a means to set a maximum when using Auto ISO. So you can now set this to the number you determined with the test above.

Practical Conclusions

Three Asian woman review an image on a DSLR monitor - ISO

ISO 320

Adjusting your ISO setting is generally only necessary when you want to achieve a specific effect or when the light conditions change.

When we do our photography workshops we always make sure to choose some locations which are outdoors and some which are indoors. This gives us the opportunity to demonstrate when it’s good to make an adjustment to the ISO setting.

Thai Wood Carver - ISO

ISO 2000 allows for a shutter speed fast enough to freeze the action in this low light setting.

If you are photographing outdoors on a bright day, your ISO setting will most likely be between ISO 100 and ISO 400. If you go inside, especially to a dimly lit building with few windows, you may find yourself struggling to obtain a good exposure with a fast enough shutter speed if you are only adjusting your aperture and shutter speed settings.

By adjusting your ISO so your camera’s sensor becomes more responsive in the low light you will be more flexible and capable of being more creative with your camera.

Read more from our Tips & Tutorials category

Kevin Landwer-Johan is a professional photographer, photography teacher, and filmmaker with over 30 years experience. Kevin is offering DPS readers his FREE course for beginner photographers which will build your confidence in photography. You will learn how to make sense of camera settings and gain a better understanding of the importance of light in photography. Check out Kevin's Critique videos where he share's his views on what's good and not so good about viewer-submitted photos.

  • capixaba

    You forgot to mention that there is a possibility of using M and auto ISO. At least on Canon cameras. I adjust aperture and speed I want for the scene and the camera gives me the ISO I have total control of what I want. I think it’s a fallacy to say that with ISO auto we have no control. The camera sets the ISO I would have to place. Likewise when they say A, Av, Tv or S are automatic modes … I use them and I have full control of my exposure … if you want some tips I’ll give.

  • Doug Sundseth

    “Using a low ISO setting will result in better technical quality photos generally.”

    I would consider motion blur and exposure to be elements of the “technical quality” of photos “generally”, so I’m afraid I’d have to disagree here. Had you said something like, “Using the lowest ISO setting appropriate for the lighting, desired depth of field, and motion in the scene will result in better technical quality photos generally”, I’d agree.

  • Wolfgang Medlitsch

    Manual mode with auto ISO is a contradiction because the camera will counterbalance Your manual settings. And there is no necessity because based on the actual ISO setting the aperture and the shutter speed are chosen.
    With time priority auto ISO may make sense because of the limited range of the aperture scale.

  • Wolfgang Medlitsch

    Changing ISO settings does not change the responsiveness of the sensor – it determines the amplification of the signals – metaphorically speaking multiplies the outcome of electron counting of pixels. Thus noise is increased and dynamic range is decreased. As noise generally is increasing with darkness it is more observed in dark areas.

  • David Gee

    ‘Using a low ISO setting will result in better technical quality photos generally. There will be little or no digital noise, the colors and contrast in your images will be better.’

    It is important to not quote a sentence out of context as you have Doug. The very next sentence explains what was meant. And the whole article goes on to talk about the various occasions occasions when a higher ISO setting is desirable and appropriate and deals with motion blur, freezing motion etc. etc. It is even positive about automatic ISO which is a difficulty for some writers.
    I thought Kevin’s article was extremely helpful.
    You have to be strong to wrote an article about ISO for DPS. It seems to be the one topic which brings the critics out of the woodwork. Thankfully we have not heard from the ‘sensor sensitivity’ element.

  • David Gee

    It isn’t a contradiction. On a Nikon in manual mode you can select your desired aperture and shutter speed and let auto ISO select an appropriate ISO sensitivity setting.

  • OldPom

    Those of us who were brought up on film cameras will appreciate that ISO approximates the old factor of ‘film speed’. But with the huge advantage that it is adjustable in camera at the point of exposing, rather than having to carry several cameras with different speed film in them. The auto ISO setting with a top limit before noise becomes obvious is my choice, great plus for electronic cameras ! Excellent article Kevin.

  • Kevin Lj

    Thanks David. I am happy you have found this article helpful. I tend not to write so much about technical subjects and always aim to be as practical as I can.

  • Kevin Lj

    Thank you OldPom. I also had the pleasure of being bought up on film cameras and appreciate the comparative luxury of being able to easily adjust my ISO setting. Glad you enjoyed the article.

  • Photobrit56

    Nicely explained Kevin I too started in the land of film what a luxury to now be able to change ISO

  • Kevin Lj

    Glad you enjoyed my article. When I made the change to digital having the ISO flexibility was one of the most wonderful things! (it still is!)

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