Z7 auto ISO seems seriously flawed

Started 4 months ago | Discussions thread
MayaTlab0 Senior Member • Posts: 2,816
Re: Z7 auto ISO seems seriously flawed

j2scriba wrote:

The strange disregard for minimum shutter speed pretty much spoils this feature. Underexposure can be fixed in post, blurred pictures cannot. Am I the only one who thinks that "No" (as in "No longer exposure than I specified") should really mean "No" in this setting?

I think that there are two things to consider in your post :

I) Sensors' linear noise behaviour above a certain ISO (invariance) and why most cameras' tendency to amplify the shot instead of boosting it after the raw file is written (with a line in the metadata indicating by how much it should be brightened) is counter-productive as it destroys highlights with no noise benefit, and

II) Auto ISO behaviour.

The first point I'd agree wholeheartedly with you but there may be some reasons why manufacturers may not go there without thinking this process through : some UI issues (if you take an ISO 1600 shot that's meant to be boosted by two stops, do you indicate it as a ISO 1600 or an ISO 6400 shot ? The user needs to know at least by how much it's underexposed. Older Fuji cameras used to behave like this and displayed the resulting ISO, but not the file's real ISO value for example), some wider ecosystem issue (Lightroom didn't display older Fuji cameras' high ISO files properly at launch as the software wouldn't handle the metadata well), etc. Another point to consider is that with dual gain cameras, the notion of "base ISO" has vanished to some capacity - and what about the future ? What if we get sensors with triple, quadruple gain designs ?

Regarding the second point I prefer the way Nikon implements it. The whole point of specifying a max ISO is basically to say that above x value, the IQ is too low for you to consider the file worth it. What Nikon would tell you, if you don't like to see the camera lower the minimum shutter speed when it reaches the max ISO value you specified, is simply to raise the max ISO value if you intend to boost the file in post anyway... of course at the cost of loosing highlight information given the lack of proper implementation of the first point :D.

So I don't think that the auto ISO behaviour is flawed in regards to your concerns. The implementation of higher ISO values, above the highest base ISO value ? More like it.

The notion itself of ISO may also be questioned with digital files. Personally when I take a shot, which, let's say, requires underexposure to preserve some highlight details and then a boost in post, I'd rather know exactly how noisy the boosted areas will look than an ISO value that's lost all meaning. A sort of live view zone system with indicators for the amount of noise for each zone that would result if the darkest zone was raised above 0 would be more helpful to me in these circumstances... and even then far from perfect as I may not even want to boost the darkest parts above 0...

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