Here we are again on a perennially popular topic with an acronym suggestive of aliens from outer space.
Getting the best and most appropriate exposure for a particular shot has always been a basic technical requirement for serious photographers.
However, it needs to be stressed that the best exposure is not necessarily the exposure which maximises the photon count and produces the lowest noise in the shadows, ie. an ETTR.
The conditions for an ETTR are generally constrained by DoF requirements, subject movement and the intensity of available light (in the absence of flash).
In fact, I would say that achieving an ETTR, in the sense of maximising the photon count, may be the last consideration.
Choosing the appropriate aperture for the desired DoF, and a shutter speed sufficient to freeze both camera and subject movement, is surely of greater priority.
Only after having selected an appropriate shutter speed and aperture should one then address the implications of ETTR, which may mean increasing shutter speed at base ISO to avoid overexposure, or increasing ISO. With a camera like the D7000 or K5, there's really no need to increase ISO. If the desired aperture and minimum shutter speed for a sharp result, also result in an underexposure at base ISO, then so be it. It can't be helped.
Of course, if one has the luxury of time on one's side, if the subject is static, and the camera is on tripod, then there is surely no problem regarding 'correct' exposure.
The problem of ETTR arises when one doesn't have sufficient time to manually get the settings right for a particular scene because one is trying to 'capture the moment'. In these circumstances, an adjustable feature in the camera that would guarantee an ETTR could be useful.
However, such a feature would also have its own problems. It would be another camera adjustment to get right, and when it wasn't right, the shot might be ruined.
To give you an example. Supposing the automatic ETTR exposure adjustment was set at its maximum setting which ignores very small percentages of the frame, which we would describe as specral highlights. Supposing you are walking through the wilderness and suddenly encounter a rare or interesting bird, or animal, in the shade of some foliage, with significant areas of sky visible through the foliage.
I would suggest there would be two likely results. (1) You forget your camera is set to ignore only specral highlights for an ETTR, take the shot, the bird flies away at the sound of the shutter, and you are left with a lovely shot of deep blue sky shining through the foliage, and a noisy bird in the shadows.
(2) You remember the ETTR setting is not appropriate for the shot, and try to estimate the area of the frame that consists of bright sky which is of secondary importance, so you can make the appropriate adjustment in the camera's ETTR feature. Alas! The bird has noticed you and flies away before you take the shot.
The only solution I see to this problem is to bracket every shot you take, unless you have the luxury of time on your hands to be confident you have made the right settings for an ETTR.
There can be other advantages of bracketing exposure (or ISO) when trying to capture the moment. One of the other shots, either the overexposure or the underexposure, may be preferred irrespective of its degree of closeness to the ideal ETTR, simply because the subject has moved to a more interesting position, or adopted a more interesting facial expression during that one whole second that many cameras need for 3 frames.
