selmslie wrote:
I apparently understand it better than you or Uuglypher. I can see the fallacy. You can't (or won't).
You're massively over-complicating what is actually a rather simple technique...
ETTR is nothing more a precautionary measure... a little extra effort to avoid accidental under-exposure when using any auto exposure mode. ETTR simply says it's better to err toward slight over-exposure, than it is to under-expose. ETTR recognizes that digital imaging has some "extra headroom" in the highlights, so long as it isn't pushed too far so that they are blown out.
The reason for ETTR is that any time you need to increase or "push" exposure up in post-processing it will also dramatically increase the appearance of any noise in your image.
There will be less noise in image when exposure is "correct" or even if it's "pulled" down a little from slight over-exposure in post-processing.
ETTR isn't a perfect solution. Every shooting situation is different and it merely increases the
odds that you'll get usable images when you have to shoot with auto exposure modes.
It will also vary by manufacturer and possibly even by camera model, as well as some user techniques (such as the metering pattern they tend to use). One manufacturer might calibrate their cameras with a slight bias to over-expose, making ETTR unnecessary. Or the metering system in one model might behave differently from that in another. Or someone who uses Spot metering a lot will likely find that their need for ETTR is different from someone who uses Center Weighted or Matrix/Evaluative metering. Depending upon how the Spot metering shooter tends to use their camera, they may need more or less ETTR. It really depends upon the person.
You actually proved ETTR in your initial post. Your own statement there is that noise is slightly less in the 2nd shot where ETTR was employed, compared to the 1st shot where it wasn't. That's the whole point and purpose of ETTR.
Your shot #3 and #4 prove nothing other than that lower ISOs will always produce lower noise than high ISOs. If you have the time and means to use a lower ISO (such as a tripod and stationary subject that will wait while you set it up), that will give always give better results than a higher ISO.
And, with today's cameras, ISO 6400 that you used in your first two shots really isn't high enough to demonstrate a very significant difference.
Try using ISO 25600. Under-expose one shot and slightly over-expose (+1/3 or 2/3 stop) another.... Then "push" the under-exposed image in post processing and "pull" the over-exposed. Best to do the comparison with RAW files (so that in-camera noise reduction and sharpening are both minimized), then apply noise reduction equally to both images in post-processing. Yours may be different, but with most cameras the ETTR image will show less noise.
Any photographer who finds themselves often needing to increase the exposure in their images during post-processing should give ETTR a try to see if that helps. Someone who rarely needs to push their exposure or even tends to over-expose a lot shouldn't use it (frequent over-exposers might even try dialing in some minus Exposure Compensation... "ETTL", I suppose). Usually ETTR is only done with slight "tweaks"... +1/3 or +2/3. But some users find they need more (and some cameras are set to work in 1/2 stop increments, instead of thirds).
ETTR isn't anything new. Back in the days of film cameras a lot of us "calibrated" our own cameras, meters and even film stock using tests. For example, when shooting Fuji Velvia 50 slide film with my EOS-3 cameras, I set them to ISO 50... but with some Konica and Nikon that I used prior I would use ISO 40. Using ETTR is essentially the same thing. It is simply something folks can try, if they tend to under-expose a lot.
It will always be better when there is time to get a more exact exposure. ETTR is for fast shooting situations and only applies to auto exposure modes. And, Exposure Compensation should still be used, in addition to or "on top of" ETTR. ETTR is a "base" adjustment, while E.C. is additional fine tuning, as required by subject tonality or other factors.
So, LIGHTEN UP! (After all, that's the whole point of ETTR, to lighten up your images!
)