The Difference Between Extended ISO and Native ISO
Why cameras have Extended (or Expanded) ISO
You’ll see different types of sensor specs when looking at cameras – a native ISO range and an extended ISO range. Examples:
- My Sony a6300 has a native ISO range of 100-25,600, expandable to 51,200
- The Sony a7ii’s native ISO range is 100-25,600 but is only expandable on the low end to 50
- My new Fujifilm X-T1 has a smaller native ISO range of 200-6,400, but is expandable on the low end to 100 and up to 51,200 high
These are all great marketing tools. The more sensitive the sensor the better, right? Which certainly makes one camera better over another?
What does Extended ISO do?
Extended ISO does not make the sensor more sensitive to light.
Using extended ISO utilizes the camera processor, not the sensor, to “push” or “pull” your exposure to an equivalent ISO.
If the camera’s “native” ISO range is 100-6,400 and you set 50, the camera will overexpose the image by one stop at ISO 100 and then “pull” the exposure back one stop with the processor.
The opposite is true on the high end. If your meter calls for an ISO of 51,200 for a proper exposure but your camera’s native limit is 6,400, the camera will capture the image at ISO 6,400. Then the processor will push the exposure up three stops – from 6,400 to 12,800 to 25,600 to 51,200.
Limitations of Extended ISO
First, be aware of how your camera outputs images taken with extended ISO. My Sonys would output a RAW file while my Fuji outputs a JPG. The JPG output won’t give you any further post-processing capabilities.
Downsides of high Extended ISO
What happens when you take a very dark image in Lightroom or Photoshop and push the exposure up three stops? Noise increases significantly, especially in the shadows. Same in the camera.
Depending on your camera’s capabilities and the settings you select, the processor will run a noise reduction algorithm in the camera also.
The noise reduction will try to smooth out the “grainy” look that happens with luminance noise. This will also result in a loss of detail, and overdoing it can make the image look plasticky.
Noise reduction will also minimize color noise, the purple and green blotches, by desaturating those areas. This will also desaturate the overall colors in the photo. However, in high extended ISO, it’s virtually impossible to remove all color noise without making the image black-and-white.
Untouched RAW files:
Low Extended ISO
The only general drawback of pulling the exposure back is losing detail in the highlights. When the camera overexposes, the bright areas will be become even brighter and may wash out detail in those areas. Pulling the exposure back won’t recover those details.
Untouched RAW files:
Should You Use Extended ISO?
First of all, it depends on your camera. Know which file format your camera will use for those extended ISO captures.
If you normally shoot in JPG…
Why are you still shooting in JPG unless you’re an event or sports photographer?
Anyways, there’s nothing you can do about it, so go ahead and use extended ISO if you really need to – if there’s no other way to get more light into the sensor. Just know that the really high settings will degrade your image. Don’t overexpose the image if you’re using low extended ISO.
If you normally shoot in RAW…
I don’t see any reason to use high extended ISO. Unless you need to capture a photo now and send off the JPG immediately, like if it’ll get you a Pulitzer. Otherwise stay within your base ISO ranges and push the exposure in post where you have much better control over how it’s processed.
My Fujiflim X-T1 actually does a pretty decent job at 51,200 from its native limit of 6,400. Much better than other cameras I’ve seen that come out purple and blurry. But I still wouldn’t publish them to my portfolio. So, do some tests with your individual camera.
If your camera outputs extended ISOs in RAW, then I’d still use low extended ISO. This can be quite useful for two reasons:
- It will allow you to use a slower shutter speed if you’re looking for motion blur, like in water and clouds. You could also just overexpose the shot at the base native ISO and then pull it back in post-processing.
- Shooting at the lowest ISO possible, even the extended low ISO, will give you less noise. The difference is minimal, but if you’re going for super-detailed prints or heavy cropping, you may want to do this.
Remember to stay away from the highlights in low extended ISO.
If your camera only outputs these files in JPG, there’s no reason use low extended ISO.
Remember that extended ISO is really all about marketing.
When you’re studying camera specs, look at the native ISO. Don’t get hypnotized by the super-high extended ISO numbers.
You want to know what the hardware can do more than the software!