When looking at modern mirrorless and DSLR camera specs, you might have come across some newer terms used in the sensor sensitivity section. This refers to the ISO range of the camera, or how sensitive the sensor is to light.
These often refer to a native ISO and extended ISO range. But what does that mean?
The Short Version
Native ISO range refers to the range of ISO values that a camera sensor is designed to operate at without any additional processing or amplification. It is the range where the sensor can produce the best image quality, with optimal dynamic range and minimal noise. In this range, the sensor’s performance is optimized for a balance between signal-to-noise ratio and dynamic range.
Extended ISO range refers to the ISO values that go beyond the native sensitivity of the sensor. These values are achieved through additional processing or digital amplification of the signal after it has been converted from analog to digital. While extended ISO allows the camera to capture images in very low-light scenes, the trade-off is that image quality suffers.
The More Detailed Version
So that’s the short version. Here’s the more detailed explanation.
What is ISO?
Before we drill down further, it’s worth a quick overview of what ISO is and why it matters. If you’re used to shooting with a smartphone or point-and-shoot, you might never have had to worry about it. But it’s an essential part of photography, and as you move deeper into photography with better cameras, you’ll get much more direct control over it. It also directly affects image quality.
ISO refers to the sensitivity to light of the camera’s sensor. It’s one of the three settings that affect exposure when taking a photo. The others are aperture (size of the opening on the lens) and shutter speed (how long the sensor is exposed to light).
A low ISO corresponds to low sensitivity. So if you have ISO set to 100, you will need to either have a large aperture to let more light in, or a longer shutter speed to allow more time for the light to hit the sensor, or both.
If you use a high ISO, you can use a smaller aperture or a faster shutter speed.
So why not just use a high ISO all the time, then? It’s because there’s a crucial trade-off: the higher the ISO, the more image quality suffers. At high ISOs, you can get image noise (graininess), less accurate colors, and less detail.
Here’s a side-by-side example, with the first image at a low ISO and the second image at a very high ISO. These particular images were shot on a Fujifilm X-T5. You can see the difference even in these small versions; the larger you view them, the more obvious the problems become.
So, in general, you want the lowest ISO you can get away with.
What is Native ISO Range?
That degradation in image quality that you get at higher ISOs is the key to understanding the difference between native vs extended ISO range.
When a camera has an ISO range of, say, ISO 100 to ISO 12800, it means that those ISOs are available for shooting. But it still holds true that an image at ISO 12800 is going to have some compromises in image quality compared to the same image shot at ISO 100.
But many newer cameras take it a step further.
They have what’s known as a Native ISO range. That refers to the ISO settings that the camera’s sensor was designed to operate within. So it’s referring to the hardware’s capability.
What is Extended ISO Range?
Extended ISO range goes beyond that Native ISO range. But to do that, it has to use some in-camera digital processing. So it’s using software to boost and amplify the sensor’s capabilities.
Camera manufacturers usually do a pretty good job of tuning the camera’s built-in software to make these boosted images look their best. But the reality is that they’re pushing the sensitivity beyond what the sensor is natively capable of doing.
In practice, that usually comes with some much more drastic compromises in image quality. Once you start getting into the Extended ISO range, you often see much more prominent image noise, much less dynamic range, and much more risk of colors going a bit wonky. And it’s often quite a pronounced difference once you move from native ISO range to extended ISO range–image quality can often fall off a cliff.
Here’s a useful way to think of it. When you play music on a stereo, you can turn up the volume to a certain point and it will still sound great. But if you push it further than the speakers can naturally handle, they’ll start distorting. Yes, you’ve increased the volume and it’s louder, but the sound quality suffers. In some situations, that might not matter. But unless you really need that extra volume only occasionally, you wouldn’t put up with all that distortion in normal listening.
Cons of Using Extended ISO
Increased Image Noise & Graininess
The most noticeable problem with venturing into the extended ISO range is that the image becomes a lot grainier. You lose detail, and you start seeing noticeable artifacts in the image that reduce the image’s detail.
Decreased Dynamic Range
Dynamic range refers to the range of light and dark tones that can be captured by the camera. With an extended ISO range, the camera won’t be able to capture as much detail in the shadows and highlights, leading to a loss of detail in these areas.
Washed-out Colors
You can also find that colors start to look less natural and less rich. It might not matter so much with a nightscape of city lights, but it’ll be much more noticeable with skin colors or situations where color accuracy matters.
Pros of Using Extended ISO
So if extended ISO image quality is so bad, why use it at all?
It’s all to do with getting the shot. In very low-light conditions, it might mean the difference between getting the shot or not. And there are times that can be crucial.
While the image quality degradation in that range probably isn’t going to be much good for wedding photography or submitting to picky stock libraries, there will be plenty of times that those extreme ISOs might enable a shot for, say, a wildlife, street, or travel photographer that would have been impossible otherwise. I’m reminded of some unique footage in Planet Earth II of mobular rays feeding at night. That footage is relying on very faint bioluminescence. It’s very grainy, and, in any normal sense, the image quality is poor. But it’s showing something happening in total darkness that is simply impossible to capture otherwise and results in something truly unique. And that’s really what the extended ISO range is for. It’s there if you really need it, but for most of us, it’s not something we’d probably be shooting with every day.
It’s a good option to have available in reserve, but it’s generally best avoided most of the time.
And that’s why many camera manufacturers make it surprisingly hard to access the extended ISO. It’s often not included in the default Auto ISO presets. And on some cameras, you might even have to use a special combination of settings to be able to access it at all.
Recommendations
For most shooting, stick to the native ISO range. And even then, it’s worth testing out the higher native ISO settings to see if the results are acceptable to you. It’s an entirely subjective threshold, and every photographer is going to have their own idea of where the acceptable limit is. And some end-uses, such as stock agencies, are very particular about any kind of image noise.
Use the extended ISO range as you would a reserve tank of gas. It’s not intended for everyday use. It’s there when you can’t get what you need from the native ISO range.
Fixing High-ISO Image Flaws
I have some more detailed approaches to enhancing high-ISO images below, but a common approach that works even with old-school film is to convert the image to black and white. That masks many of the flaws, and sometimes the higher contrast and graininess of the image can become virtues.
Things Worth Knowing
- If you have the camera to output JPG images, the camera will be applying its own internal software fixes to the high-ISO images by default, and it can often very much improve the image quality through techniques such as noise reduction smoothing, and so on. On better cameras, you’ll have some control over the amount of noise reduction processing is applied.
- But you’ll into this even if you’re shooting RAW. That’s because that same processing is applied by default to the embedded JPG preview/thumbnail image that you see when you first open a RAW file. You can replace this with a non-processed version by regenerating the RAW file’s preview image in your RAW image editing app.
Fixing Image Quality Problems in Editing
And the general rule of thumb in photography is that it’s better to get the shot right at the time of capture rather than trying to fix it after. That’s a great aspiration, but it’s not always possible to do if you’re shooting in especially challenging conditions or bumping up against limitations or flaws in gear, conditions, or technique.
But it’s worth mentioning that there are some excellent tools available to help address common image quality issues with digital images. And they’re getting better and better all the time as the power of AI ramps up. They can deal remarkably well with anything from sensor issues like high-ISO image noise to lens issues like distortion, softness, vignetting, and chromatic aberration. (Note: I’m focusing here on corrections related to image quality, not image enhancement tools–that’s a different kettle of fish.)
All-round image processing apps like Lightroom Classic and Capture One have solid tools built in that are very good places to start. But it’s also possible to take it much further with more specialized tools. If you shoot in challenging conditions regularly and find room for improvement in the image quality coming out of the camera, these might well be worth a look (and they have free trials). Some are stand-alone apps; some integrate into image editing suites such as Lightroom Classic.
UPDATE: In April 2023, Adobe released an update to Lightroom Classic that added new AI-powered noise reduction for RAW files. It’s a powerful tool that rivals some of the dedicated apps below. If you’re already using Lightroom Classic for your image editing and organization, it’s well worth trying out.
Fixing Image Noise & High ISO Artifacts
- DxO PureRAW 3 (only works on RAW files, but since was updated to version 3, it has become my go-to app for this kind of thing)
- DxO DeepPrime
- Topaz Labs’ DeNoise AI
Fixing Lens-Related Optical Issues
- DxO PureRAW (again offers an impressive suite of automatic fixes that are applied before you start editing the images)
- DxO ViewPoint (correcting for lens distortion and geometry skews)
- Topaz Labs Sharpen AI (in addition to standard unsharp tools, includes focus correction and shake reduction)
