"Lets say you find that exposing plus one stop over the meter does indeed give you plenty of highlight detail to pull back in a Raw converter."
I'm not looking for more detail in the highlights. I want more detail in the lowlights, hence ETTR.
"I've actually found 1 ˝ stops on my 5D."
how did you find that extra 1 ˝ stops? I'd be interested to know. in my images, any highlights above 255 are blown out and irretrievable.
"OK so you're starting out at ISO 400 at F8 based on the meter but using ETTR which tells you you'd get better data at F5.6. Well isn't that the same as shooting at ISO 200?"
I don't think it is the same. in terms of overall exposure, it's the same. in terms of levels per stop, it's different, at least from my understanding.
let's see if I can try to explain what I'm referring to. assuming 6 stops range in my image:
stop | 6 | 5 | 4 | 3 | 2 | 1 |
levels | 128 | 256 | 512 | 1024 | 2046 | 4096 | ISO 400 ev 0.0
levels | 128 | 256 | 512 | 1024 | 2046 | 4096 | ISO 800 ev +1.0
levels | 256 | 512 | 1024 | 2046 | 4096 | ? | ISO 800 ev +1.0 adjusted back to ev 0.0 in the RAW processor
so by using ETTR, I get twice as many levels in the lowest 3 stops of data and therefore more detail in the dark areas of my images which for me is relatively important.
I could be completely wrong. one thing I'm very unsure of is whether the extra levels are preserved in the RAW Processor's output. is the converted file made up of logarithmic data which will always only preserve 128 levels in stop 6 or is the converted file made up of linear data or... ?
if I'm missing the mark, please enlighten me. I need to understand this.