Auto ETTR not very ETTR (at times)

Started by muggo, October 08, 2016, 09:42:26 PM

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muggo

I've been using ML for a while now & wouldn't be without it.  It's a great add on for my 6D.
I use Dual ISO when I need it but use Auto ETTR all the time.

However, I do have a problem with Auto ETTR that I could use some help with:
Quite often I can take a shot where the histogram is right up to the right and not blowing highlights but Auto Snap will take another shot, usually reducing the exposure time resulting in an image where the histogram is quite a way from the right.  On the final shot, histogram on camera & in Lightroom agree it's not optimally exposed (ETTR).
It happens regularly against a bright sky but often happens in less challenging exposures too.  Very often I ignore the final Auto Snap shot in favour of the one before it when processing in LR.
In brief, I take a perfect ETTR exposure & Auto ETTR decides it's too bright & takes another giving a non ETTR image.

I only take still shots, don't use LV & have Mids at 6 & Shadows at 2.  Highlight ignore is at .5% (but I have experimented with increasing this to no avail).
Please don't suggest I switch off Auto Snap & check every exposure as Auto Snap is the method I prefer to use to save time.

Any advice gratefully received.



a1ex

Since it happens on bright sky, it's unlikely to be specular highlights (this explains why increasing highlight ignore didn't help).

However, by default, highlights are placed at -1 EV. For your use case, changing it to -0.5 EV is probably better.

FYI, the downsides of this are:
- less info about how much to go back, in case of overexposure (it may require one extra test image)
- less headroom for dynamic scenes (if your scene gets brighter since last metering)

Allowing ETTR to clip one or more channels should also help.

Otherwise, some sample images should help better understanding what's going on.

muggo

Thanks A1ex

I've changed highlights to -0.5 EV to see if that helps.  FYI, Auto Snap often takes 3 or 4 shots rather than 2.  Not sure why.
I usually clip green channel, but for some reason it had reset to zero so I've switched it back on again.

If I still get the problem, I'm happy to post some sample images.  Will a link to Flickr work?  Not sure I can insert images here.
I can post unprocessed shots & label them as Auto ETTR 1 & 2 (etc) if that will do?
I shoot in RAW so can post this type or jpg as you advise.

muggo

I'm pleased to report that setting Highlights to -0.5% EV worked for me.
I still sometimes process the penultimate shot in the Snap series, but much less often.

Thanks again for your advice.
Regards
Paul