Camera settings can be a bit esoteric, and ISO is one that a lot of people don’t really understand. But knowing when to adjust it can make a huge difference to your photography. Automatic mode will make adjustments for you, but learning to adjust ISO yourself is a big step toward taking full control of your camera.
What is ISO?
Let’s get a really common question out of the way: ISO doesn’t stand for anything. Or at least anything useful. The International Standards Organization (ISO) has a standard for measuring film sensitivity, and that’s what determines the ISO value of a particular photo (just like ISO images; they’re named the same way). The calculation of the ISO value is really complicated, but you can read all about it on Wikipedia if you want to know more.
To greatly simplify the definition, ISO is how sensitive your camera is to light. A camera that is highly sensitive will pick up more details from a dark scene than one that’s less sensitive. However, this increased sensitivity comes with a cost; you get a lot more “noise,” or seemingly random visual distortion. It’s a lot like film grain in old film photos. With a high ISO, you trade some image quality (in the form of increased noise) for increased detail in a dark scene.
You can see this type of noise in the image below (this is significantly zoomed in; you usually won’t see it quite this clearly in a full photograph).
ISO isn’t the only culprit when it comes to noisy photos; sensor size, shutter speed, and other factors also come into play, but your camera’s sensitivity is the main determining factor. Getting the proper ISO will help you take pictures that capture a lot of detail without introducing too much noise. It’s a bit of a balancing act, but with some practice, you’ll get really good at choosing the right ISO for every photo.
Some General Guidelines
It’s tough to give specific ranges for ISO, as the proper sensitivity depends on the light in your photo. But there are a few things you can keep in mind while setting up your shot that will help you get the clearest, most detailed images possible.
Use as low an ISO as you can. Jamming the ISO up as high as possible will certainly let you capture the most detail in very dark parts of your photo, but it will also add a lot of grain to other areas of the image and could cause the lighter sections to become totally blown out.
Use a tripod. This is good advice for photography in general, but it’s especially useful when you’re capturing low-light photos and you don’t want to add noise in the form of grain. If your ISO is getting to the 800+ range, consider backing it down and using a tripod with a shutter speed of 1/25 or slower instead.
High ISO is useful for quick shots. If you’re trying to capture something that’s moving fast or happening over the course of a fraction of a second (think blowing out candles on a cake), a high ISO is going to be useful, as it allows you to get a quick shot without sacrificing too much detail.
Don’t get in trouble with flash. Many places, like museums and churches, don’t allow flash. If you still want to get good shots, you might need to turn up your ISO. The photos might be a little grainy, but it’s often better to capture a grainy photo than nothing at all!
Some Examples of ISO
To give you an idea of how you might want to adjust your ISO, I’ve included a number of photos that have different ISO values. This should help give you an idea of how to think about ISO and the other factors that affect it.
The image above was shot at ISO 400, which is pretty low for a photo this dark. However, the shutter speed was 1/6, which is very long. You’d need a tripod for this long of an exposure. You’ll notice that there’s not a lot of noise in the photo — the black background is very uniformly black. The lower ISO setting for this picture helped in creating a nice, smooth background without distortion.
If your subject is in motion, and you don’t want to blur the photo, you’re going to need a faster shutter speed and, if you’re working with low light, that means you’ll want a correspondingly high ISO. The image above was created using an ISO of 3200 and a shutter speed of 1/13, which is still fairly long. Because of the very dark scene, however, a higher ISO enabled the photographer to get more detail in the photo without motion blur.
On the other side of the spectrum, we have the picture above. This scene has plenty of natural light, so the photographer used a very low ISO of 50. The shutter speed was 1/160, which let in just enough light to prevent the highlights from being blown out.
Even when you do have plenty of light — such as at this track meet — you might have to bump up your ISO a bit. To keep these runners from being blurry, this photographer used a shutter speed of 1/2000, which doesn’t let much light into the sensor. To compensate for the quick shutter speed, he used an ISO of 200. Not very high, but higher than the previous photo.
The photo above was taken with an ISO of 800, which is starting to get into the “dangerously high” range. However, because the picture was taken without flash and the scene is quite dark, the increased ISO is warranted. It’s possible that flash wasn’t allowed in this building, leaving an ISO increase as the only option for capturing the scene.
Like anything else in photography, the best way to learn about ISO is to play around with it. Take the same picture with several different ISOs and see what happens. Try turning it way up, try turning it way down, and compare the results. Eventually you’ll learn to fine-tune your ISO so you get the best exposure every time.