(Auto) ETTR (Exposure to the Right): -- History & Beginners Guide

[UncleChip]

hi
just getting my head around this so sorry if its basic stuff,

canon 5dmkii,
using the set button i get an "ettr failed" message no matter what settings i change, it is working in snap and always on mode,

when you have the link to dual-iso feature enabled switched on, am i correct in my understanding that it will only use the dual-iso feature if required? for this i am thinking of workflow, if half a set of images are dual-iso and half are not,

[ironmarshal]

If I'm understanding this correctly, the ETTR function adjusts both shutter and ISO. You set the minimum shutter speed in the settings and it determines the optimal settings. How does this compare to setting both shutter and aperture and using Auto ISO from an image quality perspective?

[aulden]

Im having issues with ETTR set to always on when using the new 3.5k mode (5x zoom) in  the experimental croprec build. It doesnt adjust.

Any ideas? Setting it to "SET" works fine but i noticed that it zooms out from the 5x, then back. Perhaps its not compatible with zoomed liveview recording modes?

Im using the 5D III and magiclantern-crop_rec_4k.2017Oct16.5D3113

[c_joerg]

I’m a little bit confused using AV Mode on 6D. Does ETTR only works on M Mode?
Wiki says ‘Put the camera in manual M mode or Av mode’
What about drive modes. Can I use Silent mode or self-timer for ETTR?

[a1ex]

It used to work in Av, but results were far from great (it was more like two very different metering methods fighting each other).

All drive modes should work fine, as long as you don't expect metering during a burst sequence (for now).

[c_joerg]

Thanks for answer…

What is that supposed to mean?
‘the image is displayed in the LCD monitor with an analysis of the image’

On CHDK I used a RAW meter which analyzed the raw data with a histogram on 14bit RAW Data. The exposure for the following shoots has been corrected with this information. Is this something similar?

[a1ex]

If in doubt, check ML help at the bottom of screen (that one is usually up to date).

Yes, this adjusts exposure for the next image, based on the raw histogram of previous image. Alternatively, it can meter from LiveView, but that's a bit of hit and miss, as raw exposure in LiveView doesn't quite match the one from CR2 and the exact amount may be model-specific.

[keepersdungeon]

I'm doing some tests with Auto ETTR, but It's resetting the slowest shutter by itself, I'm not sure why though.
Using on Canon 6D 1.1.6
Tried with nightly build feb04 and experimental 10bit_12bit jan31.
Both same result, here's what I'm doing.
Active ETTR, go to live view set the slowest, (ettr<=10" displayed on screen) take 1st shot, all good displays that it's settled to(...) but after taking a couple while moving (3-4) it changes the slowest shutter speed to the current speed and starts going up on the iso.

Hope this is clear, any idea what I'm doing wrong?
Thanks

Sent from my Pixel using Tapatalk

[a1ex]

If you upload some LiveView frames (simple silent pictures) from the LiveView scene you are metering, it might become clear.

Best guess: at long exposure times, it might have something to do with how Canon code implements exposure simulation. It's hard to preview a 10-second exposure from a 1/30 LiveView frame, let alone meter the optimal exposure from it. If, after a certain exposure level, the LiveView does not brighten any more, or if the brightening is applied in the processing pipeline after the raw data (happens at very long exposures), Auto ETTR may believe the image is underexposed and keep raising the exposure settings. One such register was recently identified, but ETTR wasn't updated to make use of it.

For long exposures, try metering from actual images (outside LiveView).

If you are not metering a long exposure, the white level might be wrong; in this case, please run this test:
http://www.magiclantern.fm/forum/index.php?topic=16054.msg195395#msg195395

[keepersdungeon]

If, after a certain exposure level, the LiveView does not brighten any more, or if the brightening is applied in the processing pipeline after the raw data (happens at very long exposures), Auto ETTR may believe the image is underexposed and keep raising the exposure settings.

Yeah I though of that but actually i'm not doing 10 second exposure i'm just setting the maximum slow shutter for the AETTR, and the prob is that when the image gets a bit dark instead of having slower shutter speed it's resetting the value I set it in the begging and it's raising the ISO. I also tried setting it to 6 sec as slowest shutter speed same thing.
That raises another question, if it took a long exposure and the LiveView does not brighten any more doesn't it check the RawHistogram of the preview image after that? (histogram set to "Raw RGB"  in "draw all modes" and the "Raw EV indicato"r to "ETTR hint" mode and i have 2 sec preview) or am I just mixing everything up now?

I'm not sure what u mean with the white balance @A1ex, the images seems fine when I open them no pink pixels on anything weird.
I have a question if the overall exposure changes quickly in like 3 images could that be the reason it's behaving like that?

Thanks again for you time

[keepersdungeon]

ok if I disable "link to canon shutter" and set the slowest shutter manually it works perfectly

[elenhil]

What does the 'ETTR failed' message really mean? Does it mean that the algorithm simply cannon find an optimal setting for the scene, or that there is some genuine module error involved?

[names_are_hard]

Checking the source, there are a variety of possible causes.  The relevant code is in modules/ettr/ettr.c

There are some early ways to hit this error, shown here (similar in auto_ettr_on_request_task_slow()):

Code: [Select]

1122 static void auto_ettr_on_request_task_fast()
1123 {
1124     ettr_beep();
1125     int raw_requested = 0;
1126
1127     char* err_msg = "ETTR failed";
1128
1129     /* requires LiveView and ExpSim */
1130     if (!auto_ettr_prepare_lv(0, 1)) goto err;
1131     if (!auto_ettr_check_lv()) goto err;
1132
1133     if (get_halfshutter_pressed())
1134     {
1135         msleep(500);
1136         if (get_halfshutter_pressed()) goto err;
1137     }

There are some later ways too but that's too complex for me to try and list.

[elenhil]

Unfortunately, that doesn't explain much to me. The thing is, I'm trying to make a FRSP timelapse with DualISO. And the way ETTR turns DualISO on and off seems inconsistent (like, three shots 20 seconds apart, the first and the last ones has DualISO while the middle one doesn't). Since I can't get any kind of log, I suspect that the ones without DualISO are probably the ones with 'ETTR failed' (because that's what I get in regular photos where ETTR fails - no DualISO setting).

[names_are_hard]

Well, I answered your original question: the error message can have multiple causes, and they are complex.

It sounds like your actual problem is more likely something in DualISO than ETTR.  Maybe some interaction between the two?  I don't have any direct experience with either of these so I can't help, sorry.  If you know a little C you could add some logging.