Author Topic: ETTR changes EXP to -1 or -5 after taking pic  (Read 7231 times)

lukgier

  • New to the forum
  • *
  • Posts: 12
ETTR changes EXP to -1 or -5 after taking pic
« on: July 07, 2014, 06:14:58 PM »
Hi,

I use 5Dmk3 and started using ETTR with Dual ISO.

When I take a photo my EXP changes -1, -2 or even to -5 sometimes so next photos are quite dark and I can't figure out why it is doing so. It deosn't matter if I set EXP to 0 or +1,2 after taking a pic the EXP decreases, sometimes it's after one pic, sametimes after a couple of pics so I need to change the EXP manually.

This happens in At and Tv modes, ISO set manually, no matter if I use dual ISO or not.

Can you help me out and explain why the ETTR behaves like this?

Thanks in advance

LG

dmilligan

  • Developer
  • Hero Member
  • *****
  • Posts: 3218
  • 60Da / 1100D / EOSM
Re: ETTR changes EXP to -1 or -5 after taking pic
« Reply #1 on: July 08, 2014, 12:42:33 AM »
It's supposed to do that. It's "exposing to the right" (or trying to). In Av and Tv it does this by setting expo comp. IMO ETTR is not very useful in Av or Tv. (You're basically trying to use two conflicting metering methods together, Canon's built in metering and ETTR's metering). If you meter on a dark area, Canon's metering is probably going to blow some highlights, ETTR is then going to try and not blow those highlights, so you're probably going to get a negative EC. If you meter on a bright area, ETTR may very we'll turn up the EC.

lukgier

  • New to the forum
  • *
  • Posts: 12
Re: ETTR changes EXP to -1 or -5 after taking pic
« Reply #2 on: July 16, 2014, 12:14:28 AM »
Thank you dmilligan very much for your reply.

I switched to M mode but still have some issues and can't understand behaviour of ETTR.

I took some photos with EV 0 (link to canon shutter on, link to dual iso on)

1) shutter 1/30, ISO 3200


2) shutter 1/50, ISO 5000 /ETTR says it changes ISO for next photo to 6400


3) shutter 1/50, ISO 6400


The problem is that in my opinion the histogram doesn't look like ETTER except the first one.
Last files taken in this scene weren't recognized as DUAL ISO, so the ETTR didn't use it - but it used it for 3 above. 
Sometimes ETTER set ISO 3200 sometimes 5000 and sometimes 6400 fot the same scene and the same shutter - 1/50.

Could you explain why it is doing so, what I am doing wrong? Shouldn't ETTR set the parameters automaticly to reach for the ETTR, if so why is it not doing that what the histograms above show.

I am useing 5dm3 with the latest ML for 1.13.

The photos were taken in photo mode. Had I better use the live view mode for ETTR?

Audionut

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 3616
  • Blunt and to the point
Re: ETTR changes EXP to -1 or -5 after taking pic
« Reply #3 on: July 16, 2014, 12:47:53 AM »
1/50 - ISO 6400 is brighter then 1/30 - ISO 3200, ie:  it's been pushed further to the right.

a1ex

  • Administrator
  • Hero Member
  • *****
  • Posts: 12457
Re: ETTR changes EXP to -1 or -5 after taking pic
« Reply #4 on: July 16, 2014, 07:27:51 AM »
Ideally, ETTR should take into account the noise at each ISO, but right now it doesn't (it assumes ISO does not introduce significant noise). That's the proper thing to do at low ISOs, but not at high ISOs.

ISO 6400 1/50 is brighter than 3200 1/30, but the second one captures 1.66x more photons. The noise ratios for these 2 ISOs are 2.5 / 2.7, so ISO 3200 1/30 is cleaner by 0.62 stops.

I'll address this in a future update.

Audionut

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 3616
  • Blunt and to the point
Re: ETTR changes EXP to -1 or -5 after taking pic
« Reply #5 on: July 16, 2014, 08:10:22 AM »
One comment I have seen regarding AETTR, is that it "takes the fun out of it" lol.  For one reason or another, I always seem to manually ETTR.

Having AETTR based on noise determination would be excellent.

a1ex

  • Administrator
  • Hero Member
  • *****
  • Posts: 12457
Re: ETTR changes EXP to -1 or -5 after taking pic
« Reply #6 on: July 16, 2014, 08:17:28 AM »
That's why I have the hint always on, even if the main ETTR function is turned off :P

lukgier

  • New to the forum
  • *
  • Posts: 12
Re: ETTR changes EXP to -1 or -5 after taking pic
« Reply #7 on: July 16, 2014, 08:24:05 AM »
That's why I have the hint always on, even if the main ETTR function is turned off :P

What do you mean by "the hint"?

Thanks for answers.

What about shooting in photo and live mode?

Why ETTR somtimes uses dual ISO and sometimes not for the same scene? For example when I set manually ISO to 6400 it didn't use dual ISO but when is was at lower ISO ETTR was chaning it to higher (5K, 6400) and in that cases it was using dual.

Audionut

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 3616
  • Blunt and to the point
Re: ETTR changes EXP to -1 or -5 after taking pic
« Reply #8 on: July 16, 2014, 08:42:50 AM »
What do you mean by "the hint"?

http://www.magiclantern.fm/forum/index.php?topic=12096.0

Why ETTR somtimes uses dual ISO and sometimes not for the same scene? For example when I set manually ISO to 6400 it didn't use dual ISO but when is was at lower ISO ETTR was chaning it to higher (5K, 6400) and in that cases it was using dual.

http://www.magiclantern.fm/forum/index.php?topic=5693.0

That's why I have the hint always on, even if the main ETTR function is turned off :P

Heh, guess I should stop looking at the massive DR number.  ;D

lukgier

  • New to the forum
  • *
  • Posts: 12
Re: ETTR changes EXP to -1 or -5 after taking pic
« Reply #9 on: July 16, 2014, 09:51:59 AM »
http://www.magiclantern.fm/forum/index.php?topic=12096.0

http://www.magiclantern.fm/forum/index.php?topic=5693.0

Heh, guess I should stop looking at the massive DR number.  ;D

Thanks for the links. I've read the thread about ETTR but still can't figure out why ETTR somtimes uses dual ISO and sometimes not for the same scene :/

Does it mean that if I want to take full of ETTR I should switch to live view mode with hints? Shooting in LV is a nightmare :(

Audionut

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 3616
  • Blunt and to the point
Re: ETTR changes EXP to -1 or -5 after taking pic
« Reply #10 on: July 16, 2014, 10:31:46 AM »
How similar are the scenes?  Framing slightly different can and does cause different metering.
If you are set up on a tripod or such, without changing lighting, can you please describe a step by step process to reproduce the problem.
I haven't played with AETTR+dual_iso much, but when I did it behaved as expected here.


Raw based exposure feedback works in quick review.
They work in both Movie mode and Photo mode Live View, and in the Quick Image review.  In Movie mode Live View, you must load one of the raw recording modules for raw based exposure feedback to function.

lukgier

  • New to the forum
  • *
  • Posts: 12
Re: ETTR changes EXP to -1 or -5 after taking pic
« Reply #11 on: July 16, 2014, 10:35:26 PM »
I still can't understand why ETTR behaves so unpredictable. I took photos in variety of F - from 4 to 2.2 with speedlite 580 and flash comp. + 1/3 and + 2/3, and only the first photo at F4 looks like ETTRed, the rest doesn't at all in my opinion. And I wasn't able to repeat the first one even if I was using the same settings - it still doesn't look like the first one - ETTRed indeed.

And only the first one is dual ISO.

F4 dual ISO /before cr2hdr/ - first photo very ETTRed


The same settings but no ETTR, no dual ISO /no idea why


F2.2 and 2.5 - no ETTR, no dual ISO /no idea why




Can anyone explain what I am doing wrong, or help me understand where I make mistake.

P.S. Here is the first file after cr2hdr .. the histogram looks prety similar to the second photo /the same settings but with went out with no dual ISO.





Audionut

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 3616
  • Blunt and to the point
Re: ETTR changes EXP to -1 or -5 after taking pic
« Reply #12 on: July 17, 2014, 05:15:51 AM »
There are lots of things wrong with your process.

  • A flash is not a consistent light source.  With flash compensation, it's even worse.  Small changes in flash output will cause differences in the metered output.  And no, you're flash does not always produce the exact same level of light, even in manual mode.
  • Lightroom is not an accurate way to determine the raw exposure.  Lightroom applies non-linear processing.
  • Disregarding the point above, White Balance effects the rendered histogram.  Every single one of your examples has a different WB.
  • AETTR will not always place the exposure at the extreme right hand side of the histogram.  If it's within 0.5 EV, that's close enough.  Of course, this is also dependent on the AETTR settings you are using.
  • Your images are framed differently, with the light source pointing to/aiming from a different direction.

  • Use the raw based exposure feedback in ML.  It is more accurate.  Or use something like RawDigger.
  • Use a consistent light source.  A cloudy day is not a consistent light source, nor is a flash, nor is many other types of man made lighting depending on the shutter speed.
  • Put the camera on a tripod (or table or whatever) and do not move it in between tests.  Framing can and will effect metering.

lukgier

  • New to the forum
  • *
  • Posts: 12
Re: ETTR changes EXP to -1 or -5 after taking pic
« Reply #13 on: July 17, 2014, 08:11:56 AM »
Thank you Audionut, your guide really touches what I wanted to know and blows my doubts, now I at least know that the problem doesn't lay in AETTR but in my approach/settings.

That would be great if one day somebody prepared a little guide describing which settings should and which shouldn't be used with AETTR, or when AETTR is good to be used at all.

Audionut

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 3616
  • Blunt and to the point
Re: ETTR changes EXP to -1 or -5 after taking pic
« Reply #14 on: July 17, 2014, 08:19:00 AM »
Yeah I plan to update the AETTR guide with some useful examples, rather then just descriptions of what the options do.

I would suggest getting a clear understanding about all options, before attempting to use them together.

So turn off SNR settings in AETTR, and dual ISO linking.  This will turn AETTR into a simple ETTR based on the highlights.  So if you know what ETTR is, you should be able to work with this fairly easily.

Maybe try playing with the highlight ignore setting, to understand what it does.
Then you can try playing with the SNR settings, and understanding how they work, and how they effect the results.
Once you have this under control, it should be pretty easy to understand what linking AETTR to dual ISO is doing.

As above, you probably want to test on some consistent scene where the light and framing doesn't change.  This way you only see the changes from the options, and don't have to consider the changes because the light changed.

lukgier

  • New to the forum
  • *
  • Posts: 12
Re: ETTR changes EXP to -1 or -5 after taking pic
« Reply #15 on: July 17, 2014, 01:09:08 PM »
Thank you Audionut for your sugestions, I will do it this way as it sounds very reasonable and maybe share my expirience here so anybody could use it. Thanks once again.

lukgier

  • New to the forum
  • *
  • Posts: 12
Re: ETTR changes EXP to -1 or -5 after taking pic
« Reply #16 on: July 17, 2014, 10:41:05 PM »
Is there any way to prolonge or pause the quick image review? It disappears very quickly :/

dmilligan

  • Developer
  • Hero Member
  • *****
  • Posts: 3218
  • 60Da / 1100D / EOSM
Re: ETTR changes EXP to -1 or -5 after taking pic
« Reply #17 on: July 17, 2014, 11:01:43 PM »
Canon Menu > Image Review > Hold

lukgier

  • New to the forum
  • *
  • Posts: 12
Re: ETTR changes EXP to -1 or -5 after taking pic
« Reply #18 on: July 17, 2014, 11:14:04 PM »
Canon Menu > Image Review > Hold

Oh great, didn't know it would work with ML's overlays as well, just thoght it would only with the canon's, nice surprise.

Thanks a lot :)