How and When to Use Auto ISO

I’ve often found myself in the field working in fast-changing lighting conditions. When a high shutter speed is necessary to capture moving subjects, constantly having to monitor and change my ISO slows me down, and sometimes means I miss capturing a special moment. In situations such as this, I switch my camera to Auto ISO. If shooting in Shutter Priority mode, I can set my shutter speed to the minimum I need to ensure sharp photos. My camera will then pick an ISO to ensure it maintains that shutter speed, no matter what is happening with the light.

For example, with this photo of a pair of elephants coming straight towards me at a rapid pace in Zambia’s Lower Zambezi National Park, Auto ISO allowed me to capture this picture-perfect moment, even though the elephants were moving through constantly changing mixed shadow and light.

Elephants shot with Auto ISO
Canon 5D Mark III camera, Canon 200-400mm f/4L lens with built-in 1.4x extender, ISO 100, f/5, 1/400 second.

What is Auto ISO?

Auto ISO is a feature, common to most digital cameras, that allows the camera to automatically pick an ISO for each shot. You can use Auto ISO in Manual, Aperture Priority, or Shutter Priority mode, but it is probably most useful when using Shutter Priority mode. In Shutter Priority, you can pick the optimum shutter speed for your subject, and let the camera pick the aperture and ISO.

The default for shooting with a combination of Shutter Priority and Auto ISO is for the camera to choose the largest possible aperture first, and then increase ISO as necessary to maintain the desired shutter speed as light levels drop. For most action photography, such as wildlife and people, a shallow depth of field is often desired, but if you need a smaller aperture for more depth of field, consider shooting in Manual mode which allows you to set both shutter speed and aperture, letting the camera only pick ISO as a floating variable.

When Not to Use Auto ISO

Auto ISO is typically not ideal for types of photography that doesn’t involve capturing quick action, such as landscape, architecture, and other types of photography where aperture and depth of field are more important than shutter speed. These types of photography are often conducted in low light, and if you are working with the camera securely on a tripod, you don’t need to worry about having longer exposure times. In such circumstances, Auto ISO would try to pick a higher ISO for the low light, introducing unnecessary digital noise which compromises image quality.

Related Video: How to Choose a Tripod

Also, if you are shooting wildlife or action (where you need shallow depth of field) and working in extremely bright conditions, keep an eye on your camera settings, as the camera will select smaller apertures to maintain your chosen shutter speed if it has already selected the camera’s lowest ISO setting. In such circumstances, you might need to increase your shutter speed to be able to use larger apertures, or turn off Auto ISO altogether.

Capturing Action: Perfect for Auto ISO

When you are trying to capture moving subjects, especially when working in fast changing or low light conditions, Auto ISO can mean all the difference between missing the shot and nailing it. For this photo below of two polar bear cubs playing in the Arctic National Wildlife Refuge of the USA, I was working in mixed clouds, and light levels were changing rapidly and without warning. With my camera set to Shutter Priority to ensure I had a fast enough shutter speed to capture the action, Auto ISO automatically picked an aperture and ISO to maintain my shutter speed as the light changed. I used exposure compensation as necessary to ensure the proper exposure level.

Polar Bear Cubs shot with Auto ISO
Canon 5D Mark III camera, Canon 200-400mm f/4L lens with built-in 1.4x extender, ISO 500, f/5.6, 1/640 second.

And for the image below of a pair of blue-footed boobies in Galapagos National Park, Ecuador, even though the birds weren’t moving, my boat was getting tossed about in the waves. Shutter Priority and Auto ISO were the perfect combination to ensure I got the shot!

Blue Footed Boobies shot with Auto ISO
Canon 5D Mark III camera, Canon 200-400mm f/4L lens with built-in 1.4x extender, ISO 125, f/5.6, 1/500 second.

But what if the camera chooses a ridiculously high ISO?

If you are working in very low light, you might end up with extremely high ISO settings, creating images with too much noise to be usable. Most cameras allow you to set an upper limit to the ISO your camera chooses when working in Auto ISO mode. But I say, why bother? If you

limit your ISO range, then you won’t be able to take the photo at all; I’d rather keep shooting, and decide later if the image is usable or not. One thing you can do to avoid high ISOs and still keep shooting is to compromise and lower your shutter speed – it may mean you miss some shots because the subject is too blurry, but with any luck, a few will come out sharp.


Auto ISO is a very useful feature when photographing wildlife and action, especially in fast-changing or low light situations.


About the author: World-renowned professional photographer and Tamron Image Master Ian Plant is a frequent contributor to a number of leading photo magazines (including Outdoor Photographer, Popular Photography, and others). You can see more of Ian’s work at

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24 Responses to “How and When to Use Auto ISO”

  1. Alan bogatay

    When in S mode at 1/1000th, what “minimum” shutter speed should be specified, or doesn’t it matter since the user-specified shutter speed will always over ride any “minimum”?

    • Customer Service

      Hello Alan,

      Yes you have that right. The S or Shutter Priority Mode means exactly what you use described. The Shutter setting you pick
      becomes the primary exposure factor and it’s up to the camera to come up with the aperture setting to make the correct exposure.

      Your camera may have a minimum option but I do not think that is typical.

      When you implement S mode, depending on your camera, you may also want to watch the ISO to make sure it will be acceptable for
      noise levels if it goes higher then you expect.

      S mode is great for action images while the A mode is best for creating a mood with heavy focus fall off or an ultra sharp crisp
      high aperture look.

      Happy shooting!

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  2. Raden Adams

    great article and I started using this technique in my bird and other wildlife photography and it is great for what I shoot

    • ScottM

      A really good article. It didn’t even occur to me to use auto ISO in manual mode. Of course, what was I thinking🤔🙄

  3. Menno Lammerts van Bueren

    Hi Ian,

    Great article. Spot on!

    I use auto iso in fast paced action scenes, fast light changing conditions and when I have the camera next to me in a car ready to shoot if some scene would suddenly occur. Especially in the latter you don’t want to spend time to setup your camera. It should be ready to shoot.

    I am using Nikon (D810) and the feature that I like is that within auto iso I can set the “sensitivity”. Sensitivity sets the minimum shutter speed at any focal length. The default is 1/focal length (eg 200mm lens will keep the shutter speed on or below 1/200sec). When increasing sensitivity it will keep the shutter speed below 1/2xfocal length (eg 200mm the shutter speed will be 1/400mm or faster). The iso will be adjusted accordingly. I am using this in aperture priority mode. So set my aperure between at 2.8-5.6 to blur background, iso auto with sensitivity up one (@200mm max shutterspeed is 1/400sec). This way I almost have all shots tag sharp and can focus on the subject instead of camera settings!

    Of course when working on “slow photography” from tripod etc. I am using fixed iso (mostly 64iso in aperture mode to control depth of field and realize ultimate sharpness and long shutter speeds).

  4. Bill Nagel

    Great examples of using the Shutter Priority mode to capture movement with the constantly changing shadows and light. I will now use this — I have been using the Aperture Priority mode most of the time because of the changing light conditions and neglected photo opportunities because of the movement of the subject.

    • Tara

      Thank you for the useful information I applied it to shooting a lacrosse game.

  5. Denise

    Why do the newer cameras even offer such high ISOs. At what ISO setting does the noise start to make the image unusable?

    • Customer Service

      Thank you for commenting!
      The camera manufacturers have gone from the megapixel “wars” to the ISO “wars” to lure purchasers to purchase new camera

      I’m not saying the huge ISO settings are just a gimmick but at some point these very high ratings will appeal only to a small
      group of users.

      As you mentioned, the very high ratings come at the cost of the digital “noise” that the chips generate as a result of being
      amped up to the limit of their sensitivity. If you ever shot any film and “pushed” it very fast you will notice the very grainy film
      images resemble the very high sensitivity digital files.

      In addition to noise and loss of sharpness the overall dynamic range of the file diminishes, shadows get compressed, highlights
      get blown, and color can take some odd turns.

      That said when does it get unusable? That is a question only you can answer and it depends on a number of variables. It you
      want to test what you think it might be I recommend setting up a shot that you might find yourself needing to take in low light
      settings. Maybe it’s a evening exterior, maybe it’s covering indoor sports or night football, perhaps it’s a theater performance.

      Once you are set up, simply keep on cranking up the ISO and shoot some frames at each setting. When you download them
      view them in the final application and typical size you will use them such as: on the web, in a slide show, making prints. When you
      think the ISO degrades the image beyond was you’d like, you’ve found your high end of the ISO range.

      I’d recommend noting that somewhere, in your phone, in your camera bag etc, so when the time comes that you need to
      use that super fast iso you’ll know exactly what setting to use.

      Happy Shooting!

    • Ian Plant

      Hi Denise, it depends on the camera. For my Canon 5D Mark III camera, I find that even 3200 ISO can result in very clean files, if exposed properly. For high end Nikon or Sony users, the results are even better! Full frame cameras tend to have better high ISO performance than crop sensor cameras.

  6. Crunch Hardtack

    Thank you Ian for your short, but chock full o’ info article. I’ve been averse to using Auto ISO in the past, but with the info you’ve provided, I will certainly try it. I had an instance shooting flying pelicans along the SoCal coast. In my position, they would fly past right about eye level, of which the background changed from bright sunlit water to dark, in the shade cliff sides. Needless to say, it was challenging.

  7. Michael Miller

    I think the manual setting with your need of shutter speed AND f stop, with Auto ISO would work better. This way you can set your desired shutter speed and minimum f stop for some depth of field that you may need, and have the ISO pick up the difference. I do understand that this will result in higher ISO’s than the author suggested. But, with the camera picking the lowest f stop number, you are locked into minimum depth of field.

    BTW, the page would not accept the URL of

    • Ian Plant

      Hi Michael, I sometimes use manual mode, when both aperture and shutter speed are important variables for my shot. For most wildlife photography, however, the widest aperture is often the most desirable (to creatively blur the background), which is why I shoot in Shutter Priority mode most of all (in most lighting situations, the camera defaults to using the widest aperture). One challenge for Canon shooters such as myself is that when shooting in manual mode coupled with auto ISO, there is no opportunity for adjusting exposure – the camera automatically chooses a “neutral” exposure and there is no way to adjust the exposure up or down if the camera gets it wrong (any attempt to change the exposure by changing either the shutter speed or aperture results in the camera adjusting the ISO to keep the exposure the same). I don’t know if other camera systems have the same problem or not.

      • Jens

        Yes, that is really frustrating but I use spot metering and then lok the exposure for the sequence.

      • Mike

        I too use manual mode with Auto ISO on my 5diii for the reasons cited above. But to adjust the exposure, isn’t it just a matter to also set the exposure compensation +/- as required? Thanks, as always, for your amazing images and helpful tips, esp. showing your camera settings on your shots.

        • Customer Service

          Hi, Mike. When shooting in manual mode on the Canon 5DIII, exposure compensation doesn’t work-although I have heard the most recent firmware update for the camera allows you to use exposure compensation with manual mode and auto ISO (I haven’t uploaded the most recent firmware update so I can’t personally confirm this).

  8. Jeanie

    Thanks Ian, this issue just came up for me while getting shots or trying to get shots of bees on flowers?..i had iso on auto.

  9. Joe M

    I have been using this ISO Auto for years and it works great. It is great to see another photographs use it.

  10. Lisa Griffis

    Finally realized that setting a low ISO to capture detail does not work with wildlife photography unless the animal is really still and in constant light, now when have they ever cooperated to fulfill that wish? Love auto ISO!