a7S high ISO claim - - -over hyped or not ?

Started Jul 3, 2014 | Discussions thread
Rishi Sanyal
Rishi Sanyal dpreview Admin • Posts: 725
Re: a7S high ISO claim - - -over hyped or not ?

andrewD2 wrote:

DXO marks DR results are hopeless, a 5DIII still registers some info at a similar DR to a 6D but the banding of the 5DIII makes the last few stops of DR of very poor quality. Some of the Sony sensors show good detail but the limitation is colour accuracy.

I wouldn't call them hopeless, as they correlate quite well to usability of shadow detail in RAW files. For example, according to their data, base ISO DR goes as follows: a7R > a7S >> 5DIII. Which correlates exactly with my real-world experience. You do bring up a good point about banding, which make the 5DIII shadows even less useful. That's a tough problem to tackle, though.

It's THE problem.

No. It's a problem. And, trust me, not one that is lost on me, given that I use a Canon 5DIII for my people/wedding photography. Sony for everything else.

Not tackling it makes the numbers utterly worthless in the real world. They put 5DIII and 6D 0.4 stop apart. Really? Not in my tests, no where near that close. It would suggest that all you had to do to make the 5DIII's shadows as useable as the 6D's was by using an expose 1/3rd of a stop higher. Anyone with both cameras knows that is not true. So if they are miles off there why would I trust the A7r/A7s findings? I certainly have no more reason to trust it over Sony's DR value.

If you've had so much experience with these cameras, can you please enlighten us as to an exact EV cost the FPN on the 5DIII has on DR? So that we can pass that along to DxO to add simply as an offset such that their existing infrastructure of tests/metrics - which many find immensely useful - can still remain intact.

Utterly worthless? DxO data shows the Canon 5DIII a full 3 stops behind the a7R in terms of base ISO DR. Which pans out in real-world shooting, though is a bit of an underestimate b/c of the FPN you mention. Does that make it worthless? No.

If assigning some sort of EV penalty for FPN in DR measurements were that simple & widely accepted, perhaps DxO would've had a way to account for this already. If you yourself know of any such solution, please do bring it to our/their attention though.

Also - you do realize that different copies of bodies have varying degrees of FPN, right? How does one address that?

No point in talking read noise this / SNR that if you can't actually use the DR in a real image.
Why not do your own COMPARATIVE test rather than relying on DXO?


Actually, there is very much a point. B/c the general trends that emerge are entirely valid. Sure, there's an additional FPN cost for certain cameras that hurts DR a bit more. Does that make the information provided that shows a ~3 stop base ISO DR advantage for the a7R over the 5DIII useless, or the information that shows a ~1 stop base ISO DR advantage of the a7R over the a7S useless? Or are the results showing the higher ISO DR advantage of the a7S over the a7R invalid/useless? Absolutely not.

To argue that not accounting for FPN suddenly makes all the studies useless/untrustworthy is simply misleading.

By the way, do you have any idea of what the overhead of doing comparative tests between all possible combinations is? One of the major points of setting up controlled studies in the first place is so that you can meaningfully compare cameras in the future with cameras in the past. Even the high ISO one-off test I did here is not something we can continue to do in any meaningful sort of manner, which is why we're working on new in-house tests.

And, by the way, I'm going to let you in on a little secret: we don't hang on to every camera we test forever.

I'd ask that in the future, before fervently responding with all caps, to please consider these sorts of things. That said, I do agree with you that accounting for FPN in some manner would be useful. Although, more and more we're seeing manufacturers ensure that FPN is subdued to minimal levels. There will, of course, always be exceptions.


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