ISO Invariance

ISO Invariance

This week I am going to show you what ISO invariance is and why you need to know about it to get better photos. Click on the image above to watch the video.

Downloadable images

If you’re looking for the downloadable images to see for yourself, Click here

It is a dropbox file with three folders. 2 images from the canon test, 2 images from the A7iii test and then the two images below (full res Jpegs)


In layman terms, ISO is basically how sensitive the sensor is to light. It is a standard set worldwide by the international standards organisation, hence the name, and it refers to the voltage that runs across the sensor. Technically; the higher the ISO figure, the higher the voltage running across the sensor and therefore the higher the amplification of the signal.


Invariance basically means that there is no change. So ISO invariance means no change no matter what the ISO is.

What this means

In terms of cameras and their sensors, the main thing that is affected by ISO is noise… in theory a camera with ISO invariance will produce the same image with a low ISO as a high ISO …… so I’ve hired a cheap canon camera….all canon camera sensors are NOT ISO invariant, and I’m putting against my A7iii which is ISO invariant to show you the difference and why it matters, especially for astrophotography. It’s not a fair comparison camera to camera but its to show you what an ISO invariant sensor is like compared to a non ISO invariant sensor.

Now I’m trying to get my head around this so this is why I’m making this video….so I gain a really deep understanding of this. Click on the video link above to see the whole show!

I went out the other night and took a series of photos on both the A7iii and the Canon 1300D. I kept the aperture as wide as possible, the shutter speed as long as possible…..taking into consideration the 500/300 rule and then shot a sequence of images from 100 ISO to 6400 ISO. TO check these out click on this link, or the link at the top of the article.

Not ISO invariant (Canon 1300D)

ISO 100 bumped up 5 stops on left……..ISO 6400 knocked down 1 stop on right

ISO Invariant (A7iii)

ISO 100 bumped up 5 stops on left……..ISO 6400 knocked down 1 stop on right


After doing this test, I took two different shots and used light painting to light up the foreground. I then edited them in post to get the same levels. The image on the left has an ISO of 800 and the image on the right has an ISO of 5000……can you tell the difference?

So from these results you can see why ISO invariant sensors could be beneficial…. At the lower ISO’s you can bring back the exposure without inducing that horrible digital noise seen in the canon images. So if you mess it up by under exposing your shot, it doesn’t matter too much…… as long as your camera is ISO invariant.

ISO invariant

Sony A7iii, A7Rii, A7ii, A7riii

Nikon D810, D750, D7100, D5500

Pentax K5

Fuji XT1, X100, XE1

Not ISO invariant




All canon DSLRS


If you have a camera that is ISO invariant this is great news. You can under expose your image a little bit and then bring it back in post if you want to….or if you’re trying to protect your highlights. Whenever I shoot astrophotography shots now, I take one at the higher ISOs and then a few at the lower ISOs so then I have the option in post production of choosing either one or the other.

If your camera isn’t ISO invariant, it’s not the end of the world. Most cameras nowadays are amazing so all you’ll need to do is get your ISO right in camera….which is always a good idea as nothing beats proper technique.

If you’re thinking about switching from a canon to a sony…this is yet another reason to do so…..I know that the 6D and the 5D mkiv also are ISO variant….so in those cameras, you will have to shoot with higher ISOs. If you have a different camera and you’re wondering if yours is ISO invariant or not….check the list above.

Here are the links to the kit I use:

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