Welcome to the forum!

As an adjunct to the Tangents blog, the intention with this forum is to answer any questions, and allow a diverse discussion of topics related photography. With that, see it as an open invitation to just climb in and start threads and to respond to any threads.

What cameras are ISO Invariant?


The buzz for a while is the ISO-less approach to photography. I'm intrigued. I'm a Canon shooter so it hasn't applied to me !!

I'm contemplating getting the Sony AR7 II because it will allow me to use ISO-less techniques while using my current Canon lenses. Does anyone have a view on whether this lens with Sony idea is a good solution or not? I'm not keen on the Sony glass offerings at the moment 

The other idea is the Fuji X system. Are these really ISO Invariant or not? does anyone know about these things because I've read contradictory reports online. I know Neil did a review of a Fuji a while back but I don't believe he looked at this aspect of it's function. I'd be grateful for any help you could give me.

Thank you for your help


  • edited December 2015
    This was an interesting read..

    Good read:

  • Neil vNNeil vN Administrator
    I agree with this comment posted in that thread on DP Review: 

    "But...so what? Who wants to fix every low light image in post just to see if it's a keeper...or just to see it at all??

    It's the same as changing ISO. Okay. So just change the ISO because...you know...it's the same thing."
  • I do a fair bit of reading about photography and equipment, but I can't recall even hearing about "ISO invariance" before now. Or maybe I just skip over those articles. :)
  • TrevTrev Moderator
    Yep, me too Nikonguy, I had to get my mate Google tell me.

    I just don't see the point, I mean if you seeing an almost black screen on LCD, that would scare the bejeebers outta me, so why not just get it right in the first bloody place.
  • My understanding is that using this technique increases DR considerably allowing you to capture shots hitherto impossible by exposing for the highlights thus preserving them from blowing out and then raising the shadows to an acceptable lever. Have I missed something?
  • Changing the ISO wouldn't do this because you'd blow the highlights.
  • This is the first time I’ve heard of ISO invariant, it sound
    like you’re under exposing the image, exposing to the left limiting the amount
    of information the sensor is taking in. 
    Isn’t it better to expose for the high lights, expose to the right and let
    the sensor take in as much information as possible?

  • Neil vNNeil vN Administrator
    Then use proper exposure metering (including changing the ISO), and make sure you don't blow the highlights. 
  • wooster, you said "My understanding is that using this technique increases DR considerably
    allowing you to capture shots hitherto impossible by exposing for the
    highlights thus preserving them from blowing out and then raising the
    shadows to an acceptable lever. ... Changing the ISO wouldn't do this because you'd blow the highlights."

    Refer to what Neil just said. Setting ISO is part of the equation for a correct exposure.

    From my limited reading of the topic, the idea is that for "ISO invariant sensors" adjusting ISO in camera is really no different (and possibly worse) than always shooting at base ISO and adjusting exposure in post later.

    Even if it were true, it would be incredibly inconvenient to shoot like this. Even something as simple as reviewing the photo on the LCD, checking a histogram, even determining appropriate shutter speeds and apertures in the first place could be difficult if you were always shooting at base ISO and adjusting later.

    So this topic makes very little sense to me and I wouldn't base a camera purchase decision around it. My $0.02 only though.
  • It does rather make sense to get the ISO right to start with. Does a camera with this property help out at the extreme end of ISO, when I need a fast shutter speed but have low light? Or is it the case that because you are at the far end of the ISO, you have still run out of dynamic range?
  • All righty. I can see the ISO Invariance isn't favoured here. I hadn't used it but it did seem to offer  a lot of potential advantages to me. Keeping highlights then raising only the shadows giving more DR would surely be a good thing? Maybe I haven't understood it properly. :)
  • Well, I'm not sure on the question I posed above. That seems to me, to be the only real use for it. Obviously it helps if you do need to tweak in post, but otherwise correct exposure helps everyone, surely?
  • Correct exposure is great for sure. I thought the technique I mentioned would work in a situation where many cameras would struggle with DR by blowing highlights or else blocking blacks beyond recovery. Am I missing the point here? If so sorry. No matter and as I shoot with a Canon 5D3 it's academic ;) Mind you I've more recently used Fuji X ( which has loads more DR  and some leeway there.
  • edited April 2017

    ISO invariant just means that the ISO is effectively a post processing issue. 

    For example, when shooting raw, if you set the ISO at 200 on, for example, a Fuji when it really ought to have been four stops more at 3200, there will be (surprisingly) no detriment to image quality over originally working at 3200. You boost the exposure in post. If you boost the exposure in this case by four stops in post processing you are just effectively working at 3200 anyway. (It certainly won't have the image quality of a 200 iso shot.)

    Obviously working like that helps no-one and of course you should use the right ISO from the outset so that you can view the file properly on the camera, assess histograms and make a judgement of the quality / grain level of the ISO speed used. You also need to avoid over exposure.

  • Neil vNNeil vN Administrator
    What would keep me from under-exposing and then depending on my camera being ISO-invariant .... at a low ISO you are using a slower shutter speed ... and that usually has a detrimental effect on image sharpness. 

    So I would still want to use the higher, proper ISO when shooting - my images will be sharper. (Or have more DoF if that is a concern.)
  • edited April 2017

    Sorry Neil, what I wrote was maybe ambiguous. What I meant was shooting without changing the ISO to the appropriate setting and thereby not exposing correctly on the camera. 

    So in that example I used above you would still be using the higher shutter speed and same aperture as though having the camera set to 3200, but (accidentally?) having the camera set to 200.  You'd still be using the higher shutter speed but ending up with a very dark raw file due to having the ISO set wrongly. Mainly theoretical and not something anyone would do deliberately. 

    That very dark RAW file will still come up okay (with a bit of extra work) in post processing. The amount of grain and quality loss will not be hugely different from having the ISO set correctly at 3200, although the colours and saturation will need some work. Obviously the correctly set one is best but the difference is nowhere near as great as you might think, even with this extreme example.

    Overexposing though is a different matter. Once the highlights are completely burnt out they're gone.

    It's just to show, purely as a matter of interest, that these cameras don't seem to be increasing the signal gain from the sensor when you up the ISO, but rather just increase the exposure in the same way that you would in your RAW processing software.  There really is no reason to deliberately take advantage of this aspect of a camera except to know that the occasional underexposure or areas of difficult dark shadows don't have to be the end of the world.

    Sorry, I'll take my anorak off now!

  • Neil vNNeil vN Administrator
    Good point! You would actually be shooting at the faster shutter speeds! 
  • I do a reasonable piece of finding out about photography and hardware, however I can't remember in any event, catching wind of "ISO invariance" before now.
Sign In or Register to comment.