High ISO Noise
How a camera handles high ISO noise plays a large role in the perceived quality of its images.
ISO itself is a term that has been around for a long time - every film that you ever used had an ISO rating, your probably just didn't pay that much attention to what it was.
The ISO number represents the speed at which the camera's sensor absorbs light.
ISO numbers aren't just any number you can think of: there are set values that all cameras use (although not all cameras can capture the entire ISO range). Examples of ISO numbers include 100, 200, 400, 800, 1600, 3200, 6400 and 12800.
When you use high ISO numbers, the maximum shutter speed you can use is FASTER than if you use a low ISO, regardless of the amount of available light.
Take the following examples:
Even though the shutter speed numbers are dependent on the amount of available light, the higher ISO number always results in a faster shutter speed.
Well super! Who wouldn't want to have faster shutter speeds, right?
If you're not already dialed in to the whole fast-shutter movement, worry not. I'm getting to that.
Hello Fast Shutter, Goodbye Blur
If you only take photos of glaciers, mountains and other similarly stationary objects, then read no further. The issues I'm about to describe will NEVER be a problem for you.
However, if you've ever taken photos of moving subjects, and especially moving subjects in dim light, then you've had to deal with motion blur.
Motion blur appears in your photos when the shutter speed is not fast enough to freeze the motion of your subject. The first important variable here is the speed of your subject, and the second is the amount of available light.
Example: you'll have to use a faster shutter speed (say 1/2000) to freeze the motion of a car speeding past than you will to freeze the motion of a child going by on a tricycle (maybe 1/250). This example assumes that you're outdoors on a fairly bright day and can get your shutter speed going this fast.
If you are working with dim light - full shade, overcast day, late evening, or indoors - motion blur becomes even more of a problem, because in this light your max shutter speed will be fairly low. For example, let's say that you're taking photos in the late afternoon after the sun has gone down and the fastest shutter speed you can achieve is 1/30.
A shutter speed of 1/30 is not nearly fast enough to freeze a subject in motion, and it might not even be enough to freeze a subject only moving slightly.
So what do you do when you want to ensure sharp subjects even when the light is dim? The title of this page gives it away. You increase your ISO.
Fantastic - setting a high ISO ensures fast shutter speeds which in turn eliminate motion blur. So why wouldn't you just set your camera to ISO 6400 and leave it there all the time?
Like many other good deals, high ISO settings come with a catch.
Dial Down the Noise
High ISO settings not only increase your shutter speed, they also decrease the quality of the image.
When you set your camera to high ISO values, your photos look less smooth and more speckled. This speckling pattern in your photo is also called "grain" or simply "noise".
At ISO 100, you should not see any noise in your photos. By ISO 800 some speckling will be apparent, and by ISO 6400 it should definitely be visible.
When it comes to high ISO noise, not all cameras are created equal: some are better than others at keeping high ISO noise to a minimum. Each manufacturer has their own special way of handling noise, so one camera's ISO 800 may display the same amount of noise as another's ISO 3200.
Sensor size and megapixel count also play a role in high ISO noise, but I won't delve into that here. I've got a separate page on sensor sizes that digs into those details.
For now, it's enough for you to be aware that high ISO settings add visible noise to your photos, which can have a negative impact on image quality.
If you want to take photos of moving subjects - especially ones in dim light - then you'll need to use high ISO values to increase your shutter speed (which eliminates motion blur).
The higher the ISO number, the more noise you'll see in your photos.
Not all cameras have the same level of high ISO noise - some are better at suppressing the noise than others.
Mirrorless Camera Terms