Exposure Shift Even in Full Manual?

[Travis Cossel]

Is anyone else experiencing this (and have a solution for it)?

I've noticed that sometimes the exposure of a scene will shift slightly (darker or brighter) even when I'm in full manual mode on the camera and have all of my settings (ISO, shutter, aperture) set. It seems to me if everything is in manual then the exposure shouldn't ever shift at all.

Thoughts?

[Bruce Foreman]

Probably because something in the scene is changing. Cloud partially blocking the sun, or panning to a slightly brighter or slightly darker area. With shutter, aperture, and ISO (not AUTO ISO) all set to specific values your exposure itself is "locked" and does not change to accommodate changes in scene or subject brightness.

Now, if ISO is set to AUTO then exposure will adjust to changes in scene brightness.

[Travis Cossel]

I'll post a clip as an example so you can see what I'm talking about, but it's definitely not an issue of the actual light changing.

[Matthias Krause]

What lens are you using? Does it have a fixed aperature? And are you 100 percent sure that you turned the Auto ISO function off?

[Travis Cossel]

I was using a Canon 17-55 2.8 lens and the ISO was set to 100. If this had only happened once, I might suspect that maybe my ISO was accidentally set to auto (although I'm positive it wasn't). However, this has now happened several times and I'm certain it's not an auto ISO issue. We always use manual settings.

I'll be posting up the clip in question shortly.

[Travis Cossel]

So here is one of the clips where the exposure of the scene changes despite having all manual settings. Watch the sky become brighter at around the 4 second mark.

This is a password protected video on Vimeo

PASSWORD: skycenter

[Bruce Foreman]

I've watched it over and over and while I do see a slight brightening it is overall and not just the sky. Even the building gets a very slight degree brighter. Very slight.

Your dolly movement takes you from where your camera is seeing some dark shapes almost like you are inside, as you move to the left you clear those shapes and the camera is seeing predominantly out in clear daylight/sunlight. If you were getting an exposure change everything would darken overall as your exposure system started reading more "bright".

What I think you are seeing is some kind of a subtle change in scene lighting with exposure "locked". If it's usually as subtle as what I see here I wouldn't be concerned with it.

Do this. Setup a test where you can shoot something similar where you either "dolly" from dark to light like you did, or even pan from a dark shaded area to open lighter. Shoot it with ISO locked to the value that AUTO ISO would select, then reset ISO to AUTO and repeat. If the change from dark to light is significant enough you should see a definite exposure shift in AUTO ISO.

[Travis Cossel]

Oh, I know the exposure increases across the entire image. That's the problem. I just pointed out the sky because it's easiest to see it there. The exposure of the image is changing and it shouldn't be with everything in full manual. It shouldn't matter if I'm going from a dark area to a lighter area. In fact, that is one of the advantages of being all manual. You set your exposure settings and the image exposure is locked. With every videocamera I've owned in the past I've never had exposure change when all the settings were set manually.

But even then, this isn't the first time it's happened. It's happened on several different types of shots, including static shots in full sunlight and so on. So it's not the dolly movement that initiated the exposure change.

I was just informed that apparently the T2i was having issues where the exposure would change even with manual settings, and Canon apparently even released a firmware update for it. Maybe they'll do the same for the 7D?

[Bill Engeler]

I think the lightening is due to the sun reflecting off the building straight into the lens. I see a hot spot that gets brighter as you dolly into the end position. The flare is causing a slight loss of contrast.

[Travis Cossel]

That's a good guess, but it doesn't have anything to do with the reflection off of the building. The clip I posted was only half the shot. The first half starts on the opposite side and the building is in full view and yet the exposure doesn't shift until the end of the clip. Futhermore, I've had this happen on completely static shots as well, where there was no strong reflection from the sun.

Apparently switching to Zeiss lenses solves the problem, but I'm already invested in Canon. So hopefully Canon will release some firmware for the 7D to address this.

[Matthias Krause]

They just did...

[Marty Hudzik]

That was fast! :)

Seriously though, the thread was started on July 16th and the firmware update was release on July 22nd. I like that kind of turnaround. Obviously, Canon was at work on resolving this already and the timing of this thread was just coincidence....still...I have had issues with previous Canons that never got fixed so this is pretty cool. Especially since I have that same 17-55 f2.8 lens and I think I have noticed this also.

[John De Rienzo]

Make sure auto lighting optimiser is set to off as this can affect exposure even when in full manual!

[Bill Engeler]

Nothing I've seen about the firmware update indicates that it has anything to do with what happened in this shot. In any case, an unwanted auto exposure adjustment would cause the sky to darken, not lighten.

I am still of the idea that this is a lens issue.

p.s. Is the lightening as obvious without the banding? I mean when viewed on someting better than Vimeo?

[Liam Hall]

Bill, I guess you missed the first paragraph on the update page...

EOS 7D Firmware Update Version 1.2.2

Firmware changes

Firmware Version 1.2.2 incorporates the following fixes.

Fixes a phenomenon in which the set aperture moves when shooting movies in manual exposure mode using some Canon lenses (such as macro lenses).