The ONLY Reason You Should Change Your ISO

Of the three main camera settings (shutter speed, aperture, ISO), ISO is the one most shrouded in a fog of pseudo-understanding. Many people believe that ISO is something you change just because it gets dark outside or because you are stopping down your aperture. While these things might be tangentially related, they’re both cases of correlation, not causation. Nay, nine times out of 10, your ISO should be planted firmly at its lowest possible base setting. And the ONLY reason* you should ever change it is this: because you are targeting a specific shutter speed for your photo.

Now, what do I mean by that? Picture a totally static landscape, like a mountain sticking up into the clear sky. Because there’s nothing moving in the scene, the duration of your exposure becomes irrelevant. You can put your ISO at 100, your aperture at whatever you need to get good depth of field, and your shutter speed at whatever gives you a good exposure. You’re not trying to capture any motion here, so it really doesn’t matter if your shutter speed is 1/10 second, 1 second, or 100 seconds. As long as you pick a shutter speed to give you a good exposure, the outcome is going to be the same.

Static Landscape: ISO should be at its lowest setting, and your shutter speed is artistically irrelevant.

Static Landscape: ISO should be at its lowest setting and your shutter speed is artistically irrelevant.

But as soon as you have motion in your frame, shutter speed becomes an important artistic consideration. And true, to a large extent you can control your shutter speed by manipulating your aperture, but what happens when you can’t? For example, say you’re shooting a field of flowers. There’s a breeze blowing so you know you need to target a relatively fast shutter speed. The problem is, you’ve chosen an in-your-face composition and you need f/16 to get the full depth of field for the scene. At ISO 100 the resulting shutter speed is slow enough that each flower becomes a halo of motion blur. If you open up your aperture to get a quicker shutter then you will lose focus on your foreground flowers. So your only option is to increase your ISO. Which allows you to make a good exposure at a faster shutter speed.

Field of Dreams - ISO 320, f/16, 1/25 sec

Field of Dreams – ISO 320, f/16, 1/25 sec

How about another example, the classic case of changing ISO: shooting the Milky Way. Ask a random photographer why you need to change your ISO to shoot the Milky Way and that person is likely to say, “because it’s dark out, duh.” Which, while it may be true that it is dark at night, this is absolutely not the specific reason you should change your ISO. After all, even in the dark I can set my camera up at ISO 100, f/8, take an 8-hour exposure, and have that photo come out perfectly exposed. The reason you should change your ISO is because you’re targeting a specific shutter speed. The Milky Way is moving (at least, relative to us) which means, if you want to freeze it in place in your photo, you must use a shutter speed that will do just that. Otherwise it will turn out as a bunch of streaky stars.

Skipping over all the Rule of 500 stuff for shooting stars, let’s just say you need a shutter speed of 30 seconds for your shot in order to freeze the Milky Way in place. If you’re at ISO 100, even if you open up your aperture as wide as it can get, maybe f/2.8, you are likely to need a shutter speed of at least 30 minutes to get an acceptable exposure. Obviously, over that much time your Milky Way is going to look more like Milky Stripes. Since you can’t open your aperture any further, you must change your ISO to achieve your desired shutter speed. By bumping your ISO up six stops to 6400, you can now decrease your shutter speed by those same six stops: 30 min > 15 min > 8 min > 4 min > 2 min > 1 min > 30 sec.


ISO 6400, f/2.8, 30 seconds

At the end of the day, the rule for ISO is straightforward (at least for nature photography): leave your ISO at its lowest base setting and only change it when you are targeting a specific shutter speed for your photo when you can’t change your aperture.

What do you think? Are there other times when you should change your ISO, or does this simple rule cover all the bases? Let me know what you think in the comments!

*Author’s note: Ok, I suppose there are artistic reasons for wanting to change ISO, like if you want to introduce grain to your image. But, even in this case I believe it’s preferable to use a lower ISO for better image quality and then add the grain in post to your taste.

About Author Joshua Cripps

Joshua Cripps started making remarkable photos while he was still in the womb. His first significant image, titled Sonogram, was praised for its graininess, deliberate blurring of details, and gritty black and white mood. Earning two thumbs up from his parents, this photo only hinted at things to come. Since then Josh has won countless awards and accolades, including more than one “Certificate of Participation,” dozens of “Good Sportsmanship” plaques, and the coveted “Busy Bookworm” award. His mantel long ago collapsed under the weight of gold-painted, plastic trophies.

Currently Josh spends over 700 days every year in the field seeking out the finest landscapes on earth. He has a mighty beard and sings in a rich baritone. Hiking at least 45 miles to capture every photo, Josh ensures that every image he crafts represents the very heart of the wilderness. While you were reading this Joshua Cripps did 93 push-ups, won more awards, and became internationally re-renowned.

  • Clark Aungst

    I love to read advice from someone who knows how to “cut to the chase.” Instead of complex charts showing all of the dynamics of ISO/Shutter Speed/Aperture, Joshua has presented a logical yet concise rule that is easy to remember and follow. Well done…

  • My problem is that I don’t always have a tripod with me, and when I want to capture a lower light sunset, for example, ISO needs to go up for handheld shooting to keep shutter speed fast enough.

  • Barbarak

    From a novice to a pro…where does one begin selecting equipment to do great scenic photos? Signed, iso? (Impressive student)

    • Joshua Cripps

      Hi Barbara,

      Almost any SLR or mirrorless camera these days will produce sensational images. The main things you need to look for are the ability to change lenses, as well as adjust shutter speed, aperture, ISO, WB, and to shoot raw files. That’s all you need to create amazing photos; everything else is bells and whistles.

      Take care,


  • Jim

    Great article Josh. I generally shoot Manual mode with Auto ISO for the majority of the time on my Nikon d810. I’ll ride the shutter or aperture as needed to get the look I want at the lowest possible ISO setting the camera gives me as I’m panning my shots but it’s mainly when shooting sports, wildlife or any moving subjects when i don’t have time to adjust the ISO as quickly ( ie: birds in flight, etc ) Otherwise for static subjects I always try to keep it at the base ISO 64 if I can without Auto ISO adjusting shutter and aperture as needed.

    • Joshua Cripps

      Yup! As a landscape guy I never ever use Auto ISO but for high speed stuff it definitely comes in handy when you need to preserve your other settings.



  • I recently visited a spot that was only accessible by boat and there was significant surface motion, though my subject was static. A high ISO was my only option. The same applies to aerial landscape work. The beauty of the latest generation of full frame cameras like the Nikon D810 is that I have the option of shooting at ISO 800 or even 1600. I still remember Kodachrome 25 and Fuji Velvia 50. But you are right. Those are exceptions, not the norm.

    • Joshua Cripps

      And soon we’ll have clean images at night at 3200 ISO! It’s an awesome time to be a photographer.

  • Patrick OConnor

    I really like your understated bio. 😉

    • Kat

      Yes that had me giggling too

      • Joshua Cripps

        I find it’s important to stay humble in these times of self-aggrandizement. 🙂

  • Lovely shot of Aoraki Mt Cook in New Zealand, sunset I guess. There’s a classic place where you have to be ready. We arrived late afternoon, got a gorgeous shot of the mountain against a clear blue sky – next day, totally clouded in. I did get a lovely sunrise shot of the ridge to the west.

    • Joshua Cripps

      Sunset is correct! And dang, you are spot on about how quick the weather changes there. Got stuck in Mueller Hut for three days once because of that. 🙂

  • Great article Joshua! I photograph a lot of waterfalls here in New Hampshire and use ISO to manage my shutter speed to create different moods in my photos. I don’t always want a completely blurred look to the water, especially when it comes to conveying the power of the water. Since I want an aperture that will give me plenty of DoF, the only other option for speeding up the shutter is to bump the ISO.

    • Joshua Cripps

      Thanks, Jeff! Well said; photographing waterfalls is a perfect example of putting this to practice.