Shooting high ISO vs underexposing and lifting in post question

Started 3 months ago | Discussions thread
Slaginfected Contributing Member • Posts: 745
Re: "Magic handwaving" or simple physics

alanr0 wrote:

Slaginfected wrote:

J A C S wrote:

Well, it does not prove that. The A7s3 image has darker shadows and hides the noise better. Both at 12mp, they look quite similar.

Most importantly, this is one scene, one pair of cameras, one ISO, one take on what "more processing latitude" means. It proves nothing.

I mean I don't see a difference at ISO100 between a 5D3 and a D750, yet if you start underexposing and pushing things up the well known problems with the 5D3 will become visible. This doesn't make the 5D3 unusable as a camera (which is an opinion), but the D750 just has more processing latitude, obviously.

We apply the very same process at higher ISOs with A7s3 and A9, for example, and see that the A7s3 is holding things better together, which means the A7s3 has more processing latitude.

Now you are saying that applying the same process at ISO10k which you do for ISO100 is somehow not valid and the differences you see there "prove nothing". Maybe you could elaborate on that? Magic handwaving won't do, though.

Without equalising the post-processing so that the comparison images have equivalent tone black level and identical tone curves, I have no way of knowing if there is a significant difference to explain.

Regarding digital scaling of the output at ISO 100, compared with ISO 10000. At ISO 10000, the Sony sensors you referenced have very low absolute levels of read noise.

At ISO 100 the Canon 5Diii has rather high read noise, including relatively high levels of downstream conversion noise. The input-referred read noise falls roughly inversely with ISO.

In contrast, the Nikon 750D while not exactly isoless, has a much lower ISO 100 read noise, which changes much more slowly with ISO. This gives a D750 image captured at low ISO higher engineering dynamic range, and much greater processing latitude than an equivalent 5Diii image.

https://www.photonstophotos.net/Charts/RN_e.htm#Canon%20EOS%205D%20Mark%20III_14,Nikon%20D750_14,Sony%20ILCE-7SM3_14

At ISO 3200 and higher, there is little to choose between the 5Diii and D750 in terms of read noise. They are both almost-isoless, with around 2.5 e- read noise.

At ISO 10000 the recent Sony sensors have even less read noise, which is almost independent of ISO.

Explaining the difference in behaviour for Canon 5Diii at ISO 100 compared with Sony A7siii at ISO 10000 is simple physics. No magic handwaving required.

Because I'm evil, here something for you: People wrote back in the days that the D750 is better suited for low-light images than the D810. And it seems like it doesn't stop there, you see similar things being mentioned between Z6 and Z7 (and between their 2nd iteration version), between A7III and A7rIII (and also between A7rIII and A7rIV, meaning there must be a larger difference between A7III and A7rIV) etc. So ... any explanations for that?

You know, the problem here at DPR is, that quite a few people can explain you all the nitty gritty details of how a sensor works and the RAW data and a couple other things. But noone can give you even an estimate of how the SNR of the data changes / is affected by the processing of the data afterwards, numerical problems on the way, calculation error estimations etc. Because if someone were able, they would have thrown this around already, including my way. Which didn't happen so far, which you could count as a strong indication nothing like this exists. Still, that doesn't prevent people from telling me that the stuff I'm seeing when actually processing files is wrong etc. Seriously?

Plus there are quite a few questions surrounding that topic. If the results would be all the same, why do camera makers give cameras different max ISO ratings? For example, the A7 line seems to have rather consistent max ISO ratings, and they have a certain difference between them, which seems to match up, roughly, the processing latitude differences you see at higher ISOs, for example. Strange, isn't it? And there are many more such questions combined with logical reasoning which just gives strong indication that "there is something".

And while I'm throwing around questions: How much experience do you have with low-light photography? You know, short exposure times, not really ideal light, maybe even LED lights thrown into the mix, stuff like that? Higher 4 and lower 5 digit ISOs. Just wondering ...

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