Exposure Compensation

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Ozpeter

Well-known member
This was recently discussed in the low-light banding thread, but I think this post was the first to identify some unexpected behaviour with exposure compensation

http://96.30.23.131/showthread.php?p=1652245

In brief, in Creative Motion Picture shutter priority mode, if you have shutter speed set low and ISO on 1600, and it's dark enough that you can be sure aperture is already wide open, using exposure compensation you can increase the brightness of the video significantly. I think it may be intelligently turning on "night mode", which can be used for video in that scene mode, and I wouldn't be surprised if that involved monkeying with noise reduction settings on its own too.

In the same scenario, you can't actually use exposure compensation further to darken the video when it's already underexposed - it has no effect. Again, it's using its own intelligence.

I've since been testing exactly what exposure compensation does in various scenarios and it's not straightforward. If you dial in some negative exposure compensation in a medium scene, then point towards something brighter, then put the exposure compensation back to the mid point, the video does not get brighter. It seems like the compensation gets reset when the incoming light changes. The opposite is true as well, ie make a light scene darker with ec, then point towards darker area, brighten ec, video does not get brighter.

This seems to me another example of how there's no real manual mode with the GH1 - or probably any such device, as it's all fly-by-wire and what you set is filtered by the firmware, which can choose to do what you ask or do something better if it thinks it knows best.

My car's auto gearbox is much the same - it can be switched to manual, but if you don't change gear when accelerating, eventually it will do so itself to protect the engine.

Anyone else noticed anything unexpected about the way exposure compensation works? Could this be to do with the claim that GH1 ISO can be much higher than the value set?
 
Yea, the GH1 will adjust it's ISO higher than 1600 in video mode. I think it can go as far as 12800... just noise and streaks more heavy then.
 
Illya Friedman said:
See page 108 of the manual. Do not use this mode if you want full manual control. The only mode to select and be assured you have full manual control is M (Manual Exposure Mode).
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Is there a way to preview what the image will look like in this mode? I was under the impression that it was to hit the trash can key... but I just tried this and it didn't work.
 
yabyum said:
Is there a way to preview what the image will look like in this mode? I was under the impression that it was to hit the trash can key... but I just tried this and it didn't work.
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In M mode? I believe it doesn't look different, because the image in M mode is essentially the same "live" as recorded. I can't speak to a preview with one of the priority modes; I never use them. I found the other exposure setting modes unacceptable due to "auto" corrections kicking in. I only use the camera with Cinema mode exposure set to M, and iExposure turned off.

To test what I'm saying, lock down the camera and record a short clip of a static shot and play back without moving the camera, when you press the shutter release to get out of playback mode, notice how similar (rather exact) playback looks compared to the live LCD image. Now this image is only as accurate to real life as your LCD/Viewfinder is set-up... but that's a different conversation all together.
 
The only mode to select and be assured you have full manual control is M (Manual Exposure Mode).
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If the scene is lit such that you're not going to need to vary exposure during the shot indeed manual gets close to full manual control, the only remaining problem being the automatic compensation for diminishing zoom aperture which can't be turned off in any mode.
 
Hi Ozpeter,
what do you mean exactly with "automatic compensation for diminishing zoom aperture"?
Does it have to do with the kit lens, the fact that it closes the aperture, when you zoom in? Then I don't care that much, because I mostly use Sigma 3/4 lenses, with which I'm totally happy (one zoom lens, the 70-200 1:2.8 II Macro HSM, but it has a fixed aperture)
Cheers, FD
 
Hi Ozpeter,
what do you mean exactly with "automatic compensation for diminishing zoom aperture"?
Does it have to do with the kit lens, the fact that it closes the aperture, when you zoom in?
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The more you zoom the effective aperture of the kit lens (like all zooms) reduces. There seems to be some method (ISO changing?) that the GH1 uses to compensate for this during a zoom.

Set the GH1 to Creative Motion Picture Mode, "M" (manual), and put a piece of paper on a table under the light of a desk lamp. Record for a few seconds on widest angle (kit lens), then do a rapid "crash zoom" towards the paper so that it finishes filling half the picture. Just after the zoom, you'll see the image suddenly brighten, as the GH1 compensates for the sudden change in effective aperture caused by the zoom. During a slower zoom it's less noticable, but if you 'catch it out' with a fast zoom it's clearer what's going on.

Replay it on your computer if you think it's perhaps something that happens only in the viewfinder - it's clear on playback too.

If you zoom in slowly without actually recording, you can hear the lens clicking and see the brightening happen at the same time.

Given that it's maintaining brightness during a zoom, maybe it's no bad thing, except when the change is too sudden - so there should be a menu setting allowing it to be turned off.
 
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Thx Ozpeter,
that's what I thought already, just wasn't capable of expressing it like that ;)
So one more reason, why lenses with fixed (maximum) aperture are the better choise...
Now come on Panny / Olympus / Sigma, do us a favor and release some hi-quality lenses optimised for filming !

As mentioned before, I have some Sigma lenses; they're fine in itself - as long as you stay away from autofocus etc. Of course Sigma doesn't support contrast-AF so far, so in that respect it was to be expected - but strangely enough, it doesn't work very well with my Olympus DSLR (e-300) either. Found it terribly slow... That was kind of dissapointing (no big drama though, I usually work with MF).

I have one other issue, just noticed today, after another adapter (OM > 3/4) arrived: if I mount my old Zuiko 50/f1.4, the camera says something like:
Please check whether the lens is mounted correctly
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(translated from dutch by me, so I hope it makes sense ;) - and I can't seem to get rid of this message (other then in by "fleeing" in the menu, but then I can't make any movies :Drogar-BlackEye(DBG ).
The adapter is the Olympus MF1, it mounts onto the dmw-ma1 - all "official" parts... Probably this is a total newby problem / question, but I didn't find anything about it here on the forum so far, so I'd be very happy with some help.

Cheers, FD
 
FlyingDutchman, have you set the camera to "Shoot Without Lens"? I had to do that for my Nikon adapter.
 
In creative manuel mode I can adjust aperture, shutter speed and iso BUT then I can't adjust exposure, its set all the way down. Why and how can I change it like I can in every mode except M
 
In creative manuel mode I can adjust aperture, shutter speed and iso BUT then I can't adjust exposure, its set all the way down. Why and how can I change it like I can in every mode except M
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In manual mode you adjust exposure by.... adjusting exposure. In other words, set the shutter speed, aperture and ISO as you wish. The display "-3 0 +3" then shows you whether you are under or over exposing - adjust the controls until it settles on zero, unless you wish deliberately to over or under expose. It's not a control in manual mode, it's a display.
 
Got it. Thanks ozpeter. What about historigram. I have it on and manual says its supposed to look like a mountain when properly exposed. It never looks like a mountain, more like two mountains or a couple gagged peaks
 
I have it on and manual says its supposed to look like a mountain when properly exposed.
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That's probably a bit of an over-simplification - I'd suggest simply watching the historgram under conditions of obvious over- or under-exposure, and getting to know what to look for that way.
 
The histogram turns white when it thinks you've achieved proper exposure. There's an EV (exposure value) scale at the bottom of the display that reads -3...-2...-1...0...1...2...3 which is meant to tell you how much you're overexposed or underexposed. When the histogram thinks you're properly exposed it turns white.

However, that's really only a vague guideline; it uses the entire frame to gauge what the exposure is, but you might want to directly force exposure to be "proper" on a certain part of the frame... so if that's the case, you'd want to get closer to pull proper exposure, and then move back to frame the shot, etc.
 
The histogram turns white when it thinks you've achieved proper exposure.
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Heh, I'd not noticed that, thanks for the tip!

There's an EV (exposure value) scale at the bottom of the display that reads -3...-2...-1...0...1...2...3 which is meant to tell you how much you're overexposed or underexposed.
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... when in CMP mode, manual - at other times that scale's for exposure compensation, so having the histogram on and ideally showing in white is a good scheme in the absence of that scale for metering.
 
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