jimmy462
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Phillip Reeve wrote:
okay, my explanation seems to be crap.
*All images were taken at Iso 100
*I varied the shutterspeed from 1 second for the Iso 25 shot to 1/125 for the Iso 3200 shot.
*Then I compensated for the over/under-exposure in LR, to equalize the brightness
*so the "Iso 3200" shot was pushed 5 stops.
*I used M mode
Hi Phillip,
So, let's take a look at your experiment and see what it is that was accomplished. By your explanation the exposures went like this...
pseudo ISO 25 @ 1 second
50 @ 1/2
100 @ 1/4
200 @ 1/8
400 @ 1/15
800 @ 1/30
1600 @ 1/60
3200 @ 1/125
...correct? This being so, then the exposures that were ETTR in this experiment were the pseudo ISO 50 @ 1/2 second and the 25 @ 1 second images which, obviously, were over-exposed when you took them. You then created the pseudo ISO's of 50 and 25, respectively, by bringing those image exposures "down" in LR to visually match (as close as possible) the median exposure, ISO 100 @ 1/4 second.
Now, this all being correct, so far, then the rest of the images from pseudo ISO 200 @ 1/8 second up to pseudo ISO 3200 @ 1/125 second were all under-exposed when you took them—or, in this case, exposed-to-the-left (ETTL...not to be confused with E-TTL for flash metering!)—and you had to bring all of those exposures "up" in LR to, again, match (as close as possible) the median ISO 100 @ 1/4 second image.
So far, so good?!
This then makes the in-the-field SOOC exposure sequence +2, +1, 0, -1, -2, -3, -4, -5 as hiepphotog posted earlier.
And, this would then have to make the exposure compensation sequence in LR, -2, -1, 0, +1, +2, +3, +4, +5 in the attempt to create the normalized images from pseudo ISO 25 to pseudo ISO 3200.
Everyone still on-board? Great!
So, the question becomes...what should one expect to see in this sequence of images SOOC?
In a nutshell, the over-exposed images will show the data getting pushed to the "right" in the histogram with, perhaps, the highlights getting "blown" and becoming lost in pure unrecoverable white. And the under-exposed images will show the data getting pushed to the left in the histogram with, perhaps, the shadows getting "crushed" and becoming lost in pure unrecoverable black.
And then the question becomes...which of these exposure provides the most exposure latitude for the scene that has been shot? And here, a quick and simple forensic investigation reveals the truth...
Examining the OP's sequence of "normalized" images we can still see the effects of his exposure choices. The "ISO 25" (over-exposed 2-stops) image clearly shows the lost highlights we expected (note the leaf in the left column". And the "ISO 3200" (under-exposed 5-stops) no longer has enough highlight detail to bring the exposure of the leaf in the left column back up to the exposure level of the other images.
But what of the shadows? Well, I opened the OP's sequence image in an editor and then adjusted the Gamma (middle slider in the Levels histogram control) to see what was hiding in the dark area in the right column. And, what do we find, even after the OP had tried to normalize these images? That there is clearly more preserved details to be found in the shadow areas of the "ISO 25" and "ISO 50" images and that the shadow detail quickly begins to show sensor noise from the actual ISO 100 through "ISO 3200" images.
So, what's the conclusion here?
Two things...The OP has demonstrated that ETTR is an effective method for preserving shadow detail. And that employing ETTR needs to be balanced so one does not blow their highlights. For this scene an ETTR of somewhere between +1 and +2 stops would have been ideal/appropriate.
Well, that's how this ref is calling it.
Jimmy G
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