X-T5 at 12,800 ISO

Erik Baumgartner wrote:

I don't think there are multiple ways to understand it. ETTR - exposing to the right, means exactly that, exposing to the right.

It is always advantageous to maximize sensor exposure (SS/Aperture), but at anything beyond base ISO, while you still want to expose the sensor as much as possible, this isn't really ETTR anymore as you are now ISOing to the right (AKA "histogramming" to the right) which fundamentally changes the equation.

Exposing to the right is all about maximizing the signal to noise ratio and dynamic range. Recording the brightest highlights just below clipping at base ISO (ETTR) does exactly that. ISOing to the right, on the other hand, does not. While highlights to the right is generally a good idea, and it might may very well be appropriate to do this in most situations (and certainly is for jpeg shooters at DR100), by doing that in high ISO/high DR situations you are significantly limiting the dynamic range that can be captured. Exposing to the right always guarantees the maximum possible DR, but ISOing to the right does not, at higher ISOs, you can easily be sacrificing highlight headroom unnecessarily (and undesirably).

Totally agreed. We might need to split it into JPG vs RAW, as you called it "ISOing to the right" instead. ISO is not part of the exposure (triangle), it has nothing to do with ETTR.

"ISOing to the right" is what JPG shooters should keep in mind while shooting, but it doesn't apply to RAW shooters.

For RAW shooters with ISO-invariant sensors, if light is abundant to stay at base ISO, then ETTR applies (since the SS or aperture can still be adjusted so). But if there's not enough light for the required minimum SS and A, there's not much we can do to bring the exposure any further to the right. It's then just a matter of performing the amplification in camera (by raising ISO and thus clipping highlights), or doing it in post. Of course, dual-gain, which optimizes DR vs sensitivity at different ISO, is another variable to take into consideration.

ETTR simply means "don't underexpose for no reason", I think