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09-06-2013, 06:22 PM   #1
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Why no ETTR metering?

Apart from the pros and cons of shooting ETTR what I don't understand is that to the best of my knowledge no camera maker allows the option of ETTR metering on their cameras. Why? The camera already knows before you press the shutter if the highlights are beyond the DR of the sensor so I would think just a bit more programming in the OS of the camera would give us this metering.

Surely anything I can do manually with the histogram could be done automatically through camera.
What am I missing here?

09-06-2013, 06:38 PM   #2
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QuoteOriginally posted by wildman Quote
The camera already knows before you press the shutter if the highlights are beyond the DR of the sensor
How does it know that? The sensor is dark until the shutter opens.
09-06-2013, 06:49 PM   #3
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QuoteOriginally posted by SoftwareArtifex Quote
How does it know that? The sensor is dark until the shutter opens.
I presume the shutter does not need to be open...

...set the Camera to TAv mode for instance and watch the ISO go up and down as you pan across a scene. Apparently metering is active without the shutter being open.
09-06-2013, 06:51 PM   #4
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The light meter is active, but not the sensor. The camera couldn't make a histogram without actually taking an exposure.

09-06-2013, 07:02 PM   #5
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QuoteOriginally posted by SoftwareArtifex Quote
The light meter is active, but not the sensor. The camera couldn't make a histogram without actually taking an exposure.
I'm not asking it to make a histogram only for the metering to be calibrated to know when the highlights are going to be burned.
Perhaps there is some very good technical and/or expensive reasons for cameras not having the option of ETTR metering if so what are they?
09-06-2013, 07:03 PM   #6
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It would have to make a histogram internally to do that.
09-06-2013, 07:18 PM   #7
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QuoteOriginally posted by SoftwareArtifex Quote
It would have to make a histogram internally to do that.
I presume for the purposes of ETTR metering all that would need to be known is where the upper limits of photo saturation occurs on the sensor and at what level of light this state occurs with a given sensor. Both values well understood by the camera makers. The actual total hgram shape for any given scene for this purpose is irrelevant.

At least that is how I understand it.
Perhaps you know something I don't - I"m listening.
09-06-2013, 07:26 PM   #8
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The light meter only measures averages over portions of the scene. It can't read peaks to tell if there's going to be saturation.

09-06-2013, 08:00 PM   #9
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To ask the camera to do so automatically would require a lot of small regions (as pointed out above)--although I believe some higher end dslrs do matrix metering with a fairly large number of individual areas; but one could also do a picture and then have the camera use the highest values from the histogram.

But the the problem seems to me you need to decide which highlight areas you want to "blow out" [e.g., sun reflections from surfaces], and that choice is done by the photographer--having made it one spot meters the highest (lightest) region at something like +4 e.v. So you you will do the ETTR metering, in essentially auto. mode. Although there is further complication in that the maximum intensity the sensor can handle varies with the color. About 1 to 1.5 e.v. for R/G/B.
09-06-2013, 08:06 PM   #10
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Possible in liveview.
09-06-2013, 08:15 PM   #11
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QuoteOriginally posted by SoftwareArtifex Quote
The light meter only measures averages over portions of the scene. It can't read peaks to tell if there's going to be saturation.
Ok given that than because of this limitation of current metering systems ETTR metering is not commercially viable?
09-06-2013, 08:29 PM   #12
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QuoteOriginally posted by dms Quote
But the the problem seems to me you need to decide which highlight areas you want to "blow out" [
I don't think so...
When I use the conventional hgram method I'm just making sure the extreme right side of hgram is not going over the edge but I don't know nor need to know what actual area in the scene that extreme right side represents - just keep it from clipping. At least, that's how I use it.
09-06-2013, 08:59 PM   #13
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If you don't clip the areas that should do so--its not far enough to the right. And the picture will be underexposed. Again imagine sunlight reflecting off a surface (e.g., the ocean). I don't know what the reflected highlights' zone would be--but I wouldn't be surprised if it's 3 stops above the maximum value elsewhere. Or what if the scene includes intense street lights--same problem.
09-06-2013, 09:36 PM   #14
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The arguments against it could apply to any metering method. They suggest an exposure that meets a set of rules, but that isn't always the right exposure. That's why we have three metering modes and exposure compensation.

Yusuf is right that some version of live view or digital preview could do it. It would be roughly like using CDAF - slower but better accuracy. Even combine it with face detection - I want this face exposed perfectly and let everything else fall wherever.

Maybe it's only practical with a high DR/low shadow noise sensor.
09-06-2013, 09:50 PM   #15
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QuoteOriginally posted by dms Quote
If you don't clip the areas that should do so--its not far enough to the right.
In theory I understand and agree.

In practice no. In my kind of shooting, mostly birds in the wild, I just don't have the luxury of lavishing that much time on getting all the details of the tonal range of any given shot exactly right out of the box. Most of time I have been waiting for a particular species to show for hours and the most I can realistically hope for is to be 95 percent right and worry about the remaining 5 percent in PS. Nothing for hours than 50 frames in 3 mins. Realistically I just hope for things to be optimal for my particular situation not perfect. We are talking wildlife not landscape or studio work.

Last edited by wildman; 09-06-2013 at 10:58 PM.
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