Author Topic: Anyone notice 1 full stop exposure shifts during recording / AE lock setting?  (Read 18748 times)

Shield

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Normally I set the shutter to 1/50, the aperture where I want, and leave the Auto ISO "on".

Just before I hit the record button, I check my exposure, and hit the Auto-Exposure lock.  This way the ISO doesn't ramp up or down during the shot, and I get nice even exposure for the entire "take".

Tonight I checked and double checked that I hit the AE button on the 5d3 - about 30 seconds in the exposure jumped up 1 full stop (I was able to correct the portion of the series in Lightroom) and just before the end it dropped back down to the original exposure.

So my question is this - does RAW shooting ignore the AE function, or is this something I need to hit right after I start shooting?  Or is this a bug?  Using the June 3rd build.

Anyone else notice this?  The really weird thing is I was shooting in a fixed lighting scene with a constant F/2.8 lens, and I'm 100% sure I didn't touch the wheel to adjust aperture during the shot.  I did very slowly zoom in during the shot though.  Was not using 5x (1:1) mode either.

Thanks,
Shawn

Shield

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Also, I don't want this to be confused with exposure "flickering".  For 4000 frames - let's say frames 600 through 3700 were all +1 stop overexposed compared to the beginning and end.  It didn't "flicker" or anything like that.

Audionut

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I can recall exposure changing in raw video with focal length adjustments.  The exposure change was more than the DXO measurements indicate for the lens I was using.

I haven't done enough video and enough testing though, to add anything useful other then I can confirm it happens.  :-[

Shield

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Do you recall if you had locked exposure or were shooing in a 100% manual mode (i.e. fixed ISO/shutter/F-stop value) when you noticed this?  It'll be a bummer if we can't zoom ever so slightly during a shot

Audionut

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Full manual.

Shield

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Should I officially report this as a bug?

Audionut

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Here will be fine thanks Shield.  a1ex will see it and move it if required.

I just did another quick test and I'm seeing about a full stop difference on a 24-105L lens in full manual between 24mm and 105mm.

This could help in the mean time.

edit:  DXO measurement show there should only be a very minor exposure change for the lens.
http://www.dxomark.com/index.php/Lenses/Camera-Lens-Database/Canon/EF24-105mm-f-4L-IS-USM/%28camera%29/436


GregoryOfManhattan

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may be seeing this on build i made for 50D.

in ML Menus also had Canon Digital ISO -0.3
Exp. Override ON.

for example, setting exposure for sky panning down to trees and ground.
manual exposure F16, ISO 160, 1/50, 5200 White Balance
result while panning down is a brightening of the part of the scene i'd intended to be darker along with a magenta tinge appearing.
as if both exposure EV and white balance had shifted.

wondered if i were missing something or had fat fingered the * button or some other operator error.

code used was -
Sun Jun 02 13:37:24 2013 +0300
https://bitbucket.org/hudson/magic-lantern/commits/2f07464883034ef59dce9cfa83e86b672efe2561?at=unified

Audionut

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Are the manual exposure settings changing also?

gebo

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I am noticing the same thing on the 600D. The exposure seems to change randomly, but generally when I point to a dark area the exposure adjust to even darker and when I point to a bright area the exposure makes it even brighter.

I have attached an example. Exposure changes start at 0:22.


Using CanonPreGdoff + Fileplay.zip for the 600D
960x544 24fps - canon mode 1080p

a1ex

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Don't use auto exposure for raw video. Use full manual mode and maybe auto ETTR (just don't keep it always on!)

gebo

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Don't use auto exposure for raw video. Use full manual mode and maybe auto ETTR (just don't keep it always on!)

I'm not using auto exposure for raw video, at least not intentionally, is there a separate auto exposure setting for raw and for h.264?. When I shoot h.264 this doesn't happen. It's full manual all the time.

a1ex

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Are you sure it's not a postprocessing issue? Does the raw histogram flicker like that while recording?

Steven

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Which camera calibration process are you using in Lightroom/ACR right now?

squig

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gebo

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It's an ACR and  lightroom issue http://www.magiclantern.fm/forum/index.php?topic=5710.0

I read the thread. Ok. Everything indicates that it's a ACR problem. Yes it is. I ran some tests and if I don't move any slider in ACR everything works fine, no exposure shifting.
But what confuses me is that I'm using process 2010 and this still happens, so this isn't the solution, at least for me...

Levinson

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But what confuses me is that I'm using process 2010 and this still happens, so this isn't the solution, at least for me...

Yes, the same for me also regarding 2010 & 2003 - not as dramatic as 2012, but it's there.
5d3, 5d2 & 550d

Shield

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Sigh.

This is *not* the same thing as I'm talking about.  The DNG files as unprocessed are 1 stop brighter in the middle of the recording *IF* I zoom.  They haven't been brought into ANY ACR yet.
I'm not talking about the flicker.

Get a zoom lens, shoot it with fixed exposure settings, i.e. 1/50 shutter, ISO 400, F/2.8.  Zoom in and out and watch the exposure jump one full stop.

Shield

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Sometimes it's not one full stop either.  It's so strange; it's how you'd expect a lens to act if it didn't have a fixed aperture.  Like taking a kit lens from 18 to 55 mm.

This was just shot with the June 4 build - ISO 1000, 1/50, F/2.8.  All exposure settings were manually set; no auto anything.

Note the significant exposure shift.  These haven't been brought into Lightroom's ACR, so it's not a 2010/2012 process thing.


Shield

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Will re-do the test without zooming; will lock the lens @ 24mm.  I will pan from a very bright window to the dark corner of my basement.

Steven

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Photo zoom lenses have exposure hiccups if zoomed, even if they have a constant exposure.

Shield

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Photo zoom lenses have exposure hiccups if zoomed, even if they have a constant exposure.

Not in H264, and certainly not this drastically.

Shield

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I am going to try to get to the bottom of this.  It's happening not just during zooming; often it's a scene with wide dynamic range (like a normally lit room and a bright back window) and panning back and forth.
Hell I walked in front of the lens a few times and it did it too.

Tonight I will try different lenses and see if I can replicate it.  I will confess I still use the auto-ISO and hit exposure lock to lock ISO right before I hit the record button - perhaps I need to just quit being lazy and manually select the ISO.  Still always shoot in M mode though; not like I'm doing A priority or whatever.

It's frustrating after you render a long file then see at the 4:00 mark the exposure fluctuates for no good reason.

Will report back in.

Levinson

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Hi Shield.

I don't use the AE button with video, but I've experienced this drastic exposure shift several times now, though I'm not sure it is exactly what you are experiencing.

I see it in the LCD when panning from very bright to dark  or visa-versa. Once it starts to occur, it keeps doing it until I do a config reset. Strangely, it is turning the exposure up further when the camera is pointing into light, and turns it down further when pointing into darker scenes, almost like the LCD brightness was set to auto and light was hitting the LCD sensor on the back of the camera. It is in the recording at the same places. I have not touched any ACR parameters, but it is a similar phenomenon to using ACR and the 2010 or 2003 processing during light-to-dark pans (sudden big jumps or decreases in exposure where it should be gradual).

I'm always using manual mode with a set ISO.

The only consistent thing I can associate it with is that I generally notice it after using x5 or x10 recording and frame rate override (locked at 25).

Will be interesting to figure out what is causing it, though I haven't had it in 15th or 16th June build yet. I haven't tried the most recent builds yet.

5d3, 5d2 & 550d

Shield

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Well I just shot all evening and did not notice this with the June 17th build.
Only difference?  Instead of doing the auto-ISO / then hit AEL before recording, I just used ISO 100.  No idea, but I just used my variable ND filter to adjust exposure and all was well.

I will say though that the sun wasn't in the shot and/or extreme shifts from dark to light in the footage.  Will test again tomorrow.