ISO and Noise Explained for Photographers

It’s not always easy to explain, but it’s definitely easy to see. When an image has a lot of noise, it appears grainy and unclear. This happens when your camera’s ISO value is set high—the higher the ISO, the more noise. While the rule of thumb has always been to keep the ISO low for noise-free images, today’s high-tech cameras can handle it better and allow for higher, clearer ISOs. But, what is ISO, exactly? And how do you use it properly? This video explains it all here:

What is ISO?

ISO determines how sensitive your camera is to light. The higher the ISO, the less light you’ll need to take a photo.

To explain this, Wallace asks us to imagine a room that’s lit with 128 light bulbs. Just for the sake of the example, imagine we have a proper exposure at ISO 100, shooting at f/2.8 and a shutter speed of 1/60. Every time we double the ISO, the amount of light needed is cut in half. So, at ISO 200 we can get the same result with only 64 light bulbs. At ISO 400 we’d only need 32 light bulbs. At ISO 800, 16 lights, and so on.


When ISO is doubled, the amount of light needed is cut in half.

At ISO 12,800 we would only need one light bulb, and we could still shoot at f/2.8 and 1/60 of a second.

The biggest problem with shooting at such a high ISO, however, is noise.

What is Noise?

Have you ever seen a photo that just looks grainy? Everywhere you look, you see little specks, the image just isn’t clear. That’s noise.

No matter what you do, higher ISO values come with more noise.

what is iso

At ISO 12,800 you can see the grain in this image—noise.

Today, with so many technological advances with cameras, it is easier to shoot at higher ISOs without getting as much noise as we used to. Mark Wallace thinks the groundbreaking camera was the Nikon D3X and then the Canon 5D Mark III. Now there are all kinds of cameras that can shoot at high ISOs with almost zero noise.

How to Find Out What Your Camera Can Do

It’s easy to test your camera to see what ISO it is capable of shooting before you start to see noise:

  1. Go into a room in low-light and shoot a series of images, increasing your ISO with each shot.
  2. Take a look at the photos at full resolution on your computer.
  3. If ISO 6400 has too much noise for your taste but ISO 3200 looks good, then ISO 3200 is your camera’s maximum acceptable ISO value.

Don’t be afraid to crank up the ISO in low light; it can keep your shutter speeds fast and really help you improve your low light photography.

Auto ISO

You can also use the Auto ISO setting on your camera if you don’t know what ISO value to use. Your ISO will automatically adjust for correct exposure every time you take a picture. Remember, since you’re forfeiting control, you may not always get the desired affect—the ISO might go higher than you want, giving you noisy images. But, this is easier to fix than a blurry image that can’t be used at all, so it might be worth taking the chance.

“I’d rather have noisy images that I can use than a blurry image that I have to throw away.”

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