What is ISO and why is it important in photography?

The word ISO is probably familiar to anybody who has experimented with photography or even just looked at their camera settings. Why is ISO so important for getting that ideal photo, though, and what does it actually mean? Knowing ISO is essential whether you're taking photos on a sunny afternoon or attempting to capture a birthday celebration in low light.

In the most basic sense, ISO refers to your camera sensor’s sensitivity to light. A lower ISO means your camera is less sensitive to light, and a higher ISO means it’s more sensitive. Think of ISO as your camera’s built-in brightness booster. In bright conditions, you don’t need much help—so you stick with a low ISO. But when it’s dark, bumping up the ISO lets your camera “see” more. ISO, along with shutter speed and aperture, makes up the exposure triangle or the core foundation of photography. Together, these three settings determine how bright or dark your image will be.

Changing ISO is pretty straightforward, although the process can vary a little depending on your camera. On most DSLRs and mirrorless cameras, there’s a dedicated ISO button. You can also usually adjust it through your camera’s menu or quick settings screen. Some cameras have dials for easy access, while others let you tap through touchscreen controls. If you're using a smartphone with a manual or “Pro” mode, you'll likely find ISO as one of the adjustable sliders. Play around with it to instantly see how it affects your image brightness.

Different ISO levels serve different purposes. Here’s a quick breakdown of when you might use each:

This is your go-to ISO when shooting in bright daylight or with strong studio lighting. It produces the cleanest images with the least amount of grain or “noise.” Use ISO 100 when you want crisp, high-quality photos, especially for landscapes or still shots.

Perfect for overcast days, indoor settings with decent light, or when you're just losing a bit of brightness outdoors. ISO 400 offers a bit more flexibility without introducing much noise.

This is a sweet spot for indoor photography without a flash, like during events or casual portraits. It’s also great during early evening when the light is starting to fade but you still want to avoid using artificial lighting.

Now you’re getting into low-light territory. ISO 1600 is ideal for night scenes, dimly lit rooms, or capturing candlelit moments. You’ll start seeing some grain in your photo, but many modern cameras handle it pretty well.

For serious low-light challenges, like indoor sports events or night street photography, ISO 3200 comes in handy. It brightens the scene enough to freeze action or eliminate blur, though you might see noticeable noise.

This is the high ISO setting you reach for in really dark conditions; for instance, think concerts, starry skies, or emergency low-light shots. While it’s not the cleanest in terms of image quality, it can still deliver great results with some noise reduction in post-processing.

As you become accustomed to changing ISO, keep the following points in mind:

• For the available light, choose the lowest ISO possible. It keeps your photos crisp and clear.
• Don't be alarmed by high ISO. Sometimes a little noisy picture is preferable to one that is blurry due of a sluggish shutter speed.
• Check the limitations of your camera. Every camera responds to noise in a unique way. Test your equipment by taking a few pictures at different ISO settings.
• Assign ISO to shutter speed and aperture. You may change your other settings by increasing the ISO. For example, a higher ISO may enable you to freeze action with a faster shutter time.

Every shooting situation calls for different ISO strategies. Let’s look at a few:

Stick to the lowest ISO possible, typically ISO 100 because landscapes are usually shot in daylight and don’t move, you can afford to use a slow shutter speed and a tripod for maximum detail.

Portraits benefit from low to medium ISOs between 100 and 800 depending on your lighting. If you're shooting indoors or under soft window light, bumping up to ISO 400 or 800 can help keep the subject sharp without a flash.

This is where ISO shines as you might need to crank it up to 1600, 3200, or even 6400, especially if you're shooting handheld or trying to capture movement. Use the noise-reduction settings in your camera or editing software afterward to clean things up.

To freeze fast-moving subjects, you need a fast shutter speed and that often means boosting your ISO. Depending on lighting conditions, you might be working with ISO 800 to 3200 or beyond.

Many cameras today offer Auto ISO, which automatically adjusts the ISO for you based on the lighting and your shutter/aperture settings. It’s super handy, but it has its ups and downs.

Speed and convenience: You focus on the composition while your camera handles exposure.

• Great for unpredictable lighting: Perfect for events or street photography where light conditions change fast.
• Reduces risk of blur: Cameras often prioritize keeping your shutter speed fast enough.

Loss of control: Unwanted noise may come from the camera selecting a higher ISO than you would prefer.

• Inconsistency in exposure: Occasionally, the camera may misjudge the light and slightly overexpose or underexpose.
• Less intention: Using Auto ISO exclusively may hinder your ability to master manual settings or establish a certain mood.

Although ISO may appear to be simply another camera option, it has a significant impact on how your images turn out. You may gain creative control over your photos by knowing when and how to make adjustments. Experiment with different ISO settings in different lighting scenarios to see how your camera reacts and what kinds of images you obtain. Selecting the ideal ISO will eventually become as instinctive as selecting your lens or framing your image.