How to get the best raw exposure, part 2

Please, what's so important in this discussion that you are resorting to tricks? We are just talking, nothing life-threatening.

No, but "Helping David". Since we can try, why not.

I don't remember why I wrote that sentence, but I think what it is meant to convey is that with an ETTR exposure, if noise makes up, say, 1% of the data, it will be a smaller proportion of the data then when you underexpose and it makes up 20% of the data. And thus the greater the exposure, the less the noise will be visible. In effect, strong exposure drowns out the noise. It makes sense to me and thus is a useful model for me 😁

With read noise, raising ISO will only help reduce noise if the particular camera you are using does analogue amplification. And not all cameras employ this technique for their ISO dial. Also, with modern sensors, read noise is such a small component of the overall noise burden that even if you reduced it to zero, it still wouldn't make much visible difference. So not really worth worrying about. That was my take home from previous discussions.

I'm thinking a definition of ETTR may be helpful.

I find that shadow noise in high DR scenes where I'm forced to be well under the ETTR exposure at base ISO is usually less of a problem than highlight clipping, and that for the images that I consider to be of good photographic quality, photon noise is more important than read noise, even in the shadows. I do go to the lowest high conversion gain ISO in many circumstances, though.

Well, for the situations that you shoot in, you may be almost completely out of the woods as far as visible read noise differences over a range of ISO settings is concerned, but it is not happening for everyone. I can see a difference in the depth of the Canon R5's fine banding noise (single-horizontal-line blackpoint offsets with no vertical correlation) with 12-bit e-shutter vs mechanical, and HTP-vs-non-HTP, at ISO 51K.

If read noise were like a software Gaussian noise with no spatial correlation, then this would be moot, but read noise tends to have the have enough correlation that it can be visible, even when from a mathematical standpoint, it is dwarfed in quadrature. So, when I am shooting active birds with fast shutter speeds in the red-starved shade with high magnification with a relatively slow lens, HTP and 12-bit readout are both things that I try to avoid, and I don't consider the camera ISO-invariant for such purposes, even at the highest ISO settings.

I don't use that camera. I've not seen a camera with blackpoint errors like that. I don't think I've ever used ISO that high except for testing. All that can explain how we're looking at thing differently.

Are you photographing black cats in coalbins?

What you describe doesn't strike me as being a high DR scenario, which is the constraint Jim posed. If it's a dark, colorful bird in flight and strongly backlit by the sun so that most of its visible body is shaded and especially the under-wing feathers are deeply shaded but its head is drenched in sunlight, what would you do? It's a tough call for me because I find with my micro 4/3 cameras the character of the noise is visibly different between a pushed base ISO shot vs. a pseudo-ETTR'd version (same exposure but higher ISO). Not so much in any spatially correlated way, just in terms of the look and splotchiness of the "grain". My go-to noise reduction strategies tend to work a bit better on the pseudo-ETTR'd versions but admittedly the difference is usually quite subtle. On the other hand, I seem to find myself in lots of high DR scenarios where pseudo-ETTR'ing is going to be dangerous.

I read both parts of the article. I liked it, until it got to the math part at the end :)

I think I understand the concept you're explaining but is more difficult in practice. It has to be done consciously until it becomes a habit.

If you're happy with the raindrop analogy, you can safely skip the math at the end. It's there for people who want a quantitative feel for what's going on.

It is something that most people have to work with a while before it is fully internalized and you know what to do without consciously thinking about it. ETTR at base ISO is something that most folks can get their heads around without too much effort. The dim light situation is harder for some to get, and it is complicated by the fact that there are many ways of dealing with it.

All this is most difficult for people who started out with film, or those who have bought into the whole exposure triangle nonsense.

When the film is fresh, the meter is OK, scene to be captured is within 7-8 stops, metering technique is adequate (and for most part, from my lab days, it is hit and miss), and the exposed film is to be processed through manufacturer's first choice developer, close to the time of shooting - rating on the box can be taken as a very good guide.

The question of low light in itself is not more complicated per se. But the implementation is more nuanced depending on individual needs and priorities.

Basically it boils down to priorities. Do you want to aim for technically best raw files from an exposure point of view? Or the fastest way of working with minimal changes between lighting and shooting scenarios? Maybe a faster workflow and not changing settings leads to more decisive moment keepers and so on. Or a bit of both.

The logical next step is some threads about relating all this back to various genres and strategy options, with the pros and cons for each.

For one thing, it provides greater safety than full-manual in rapidly changing light. Set full-manual for the sun or the shade, and then all of a sudden you're several stops off if your next shot is in the opposite illumination, resulting in egregious clipping or excess read noise, with many cameras. With auto-ISO, you'll only be off by the range in which you might make "EC" adjustments but failed to do so, a much smaller range of error.

There is still the issue, of course, of having the Av and Tv values set in a way that the lighting forces clipping, and I am an advocate of camera options to raise shutter speed to avoid clipping with M mode or an otherwise M-like mode.

Given the persistent disagreement with my explanation of how cameras works occuring in this thread, the thought of doing something with far more moving parts and ill-defined boundary conditions fills me with despair. At the very minimum, I would expect it to be freighted with aggressively-voiced noise, and in the absence of threaded view, it would be hard for readers to perform the necessary winnowing.

It does the same thing for OOC JPEG lightness that automation does in Av, Tv, and P modes (but these may actually vary exposure to achieve that). The EC control also does the same, but it is not actually varying exposure, but ISO setting, and therefore, default lightness.