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Old April 21st, 2012, 07:38 AM   #1
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Knowing what the auto ISO is on

Anyway to know what the auto ISO setting is on a file that has been recorded on the GH2? I've tried playing it back in the GH2 and pushing display and other buttons but can't get any info.

Went to a rehearsal last night and I will be placing the GH2 unmanned near the alter and the lighting will cahnge more then once during the ceremony. I took some test video in "S" mode with auto ISO and would like to know what's going on.
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Old April 21st, 2012, 09:27 AM   #2
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Re: Knowing what the auto ISO is on

Tim, auto ISO works differently in different situations, depending on the settings of the cam. Look in the manual for details, it's discussed there. It's limited to different values depending on your mode, or something like that. I forget the details.
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Old April 21st, 2012, 09:34 AM   #3
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Re: Knowing what the auto ISO is on

But no way to know what a scene has been shot in?
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Old April 21st, 2012, 09:48 AM   #4
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Re: Knowing what the auto ISO is on

Tim,

Unfortunately, there is no metadata available for GH2 video files. However, you can take a reference image (photo) before recording. The image will contain the metadata you seek.
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Old April 21st, 2012, 09:57 AM   #5
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Re: Knowing what the auto ISO is on

Ah, wish I would have know that last night.....thanks
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Old April 21st, 2012, 02:53 PM   #6
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Re: Knowing what the auto ISO is on

Tim, if you know the limits in effect in the mode you shot in, you can know the maximum ISO value it could have been, if that would help. It's relatively low in the auto modes/ p mode, etc. I think, but as I said earlier I forget the details.
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Old May 1st, 2012, 01:55 PM   #7
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Re: Knowing what the auto ISO is on

Quote:
Originally Posted by Jeff Harper View Post
Tim, if you know the limits in effect in the mode you shot in, you can know the maximum ISO value it could have been, if that would help. It's relatively low in the auto modes/ p mode, etc. I think, but as I said earlier I forget the details.
Good point Jeff. What is the highest useable ISO you would safely set as your upper limit? I imagine keeping this set at 3200 would result in some pretty grainy video in auto ISO situations.

Thanks,
Angelo
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Old May 1st, 2012, 02:05 PM   #8
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Re: Knowing what the auto ISO is on

I really don't know Angelo. I personally run in P mode and I adjust shutter speed and exposure with the wheel as needed, I just leave ISO alone and let it do what it will. I use only lenses that are F/2.0 or faster most the time now, so my ISO is going to be fine most of the time. I shoot weddings and run 4 cams, and I don't adjust anything that I can leave alone most times. When I have a lot of time I'll sometimes adjust the ISO, but it's not often.

Depressing the wheel, as I'm sure you know, allows us to change the ratio of shutter speed and exposure when in P mode while recording, and I use that feature a lot to control depth of field and exposure when I'm on the fly, or to over-expose for backlighting.
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Old May 2nd, 2012, 05:19 AM   #9
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Re: Knowing what the auto ISO is on

Quote:
Originally Posted by Angelo Ucciferri View Post
Good point Jeff. What is the highest useable ISO you would safely set as your upper limit? I imagine keeping this set at 3200 would result in some pretty grainy video in auto ISO situations.

Thanks,
Angelo
The noise level depends on a lot of things Angelo....including the patch used. Some like Sedna are finer grained than others.
3200 is about top for any of them.

The GH2's have an ISO bug. The top row of settings (160...) will produce noise unless you set it for a higher setting first.

I have enough to fiddle with so I just use the middle and bottom row (starting with 200).

Since I'm always after shots that have to be taken NOW, I don't worry about noise. Neat Video gets most of it in post.

I decide what DOF I need, then base the shutter speed (I don't always stay at 180 degrees) and ISO on what it takes to expose that.
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Old May 6th, 2012, 05:56 PM   #10
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Re: Knowing what the auto ISO is on

Don,

Our GH2's don't have the mechanical rotating shutter that "rule" came from. So the 180 degrees thing is totally meaningless as is the "religious" 1/48th second shutter speed "Holy Grail". In the early film days 24 fps was settled on as the frame rate that was the best compromise between economy of film consumption and enough persistence of vision effect so "motion" could be percieved with little "flicker" for most people.

At 24 fps, the rotating disk shutter had half of it's diameter "cut out" to expose the film frame. The "solid" part of the shutter disk masked the film while the next frame was pulled into place.

At 24 fps the "180 cutout" resulted in a 1/48th second shutter speed. Later "variable angle" rotating shutters could close off more of that 180 cutout for a 90 degree cutout resulting in 1/96th second and on.

None of which applies or works the same in our gear with "sensor scanning" shutters. 1/50th allows almost identical to 1/48th motion blur, no practical difference whatsoever. 1/60 for us in NTSC land allows close enough motion blur and reduces problems with artificial light on 60Hz powerline frequency.

So that 180 degree "rule" is really meaningless to us. We have other things we have to watch our for like rolling shutter effects.

But I'm definitely going to have to try the "P Mode" method you guys describe.
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Old May 8th, 2012, 01:21 PM   #11
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Re: Knowing what the auto ISO is on

Quote:
Originally Posted by Don Litten View Post
The GH2's have an ISO bug. The top row of settings (160...) will produce noise unless you set it for a higher setting first..
Wow...this is interesting. Is this a fact? I've never heard about this one.

Do we know if the new firmware fixes this issue?

By the way, I did my own ISO test shooting at night in a dark parking lot with only 1 streetlamp providing illumination. I consider this the most extreme case of high ISO shooting (pitch black w/ 1 bright source). The gradient formed from the streetlamp - was very grainy above ISO 1000. So I am going to do everything I can to keep it at or under 1000. I'd rather run a 1/25 shutter speed (assuming there is no fast motion) than go above 1000 ISO in this sort of scenario. If it was a brighter scene (like a city street with lots of ambient light and not too much gradient shadows) - I would probably go up to 1200. My test was with the factory firmware.

I was chatting with DP Philip Bloom at a conference this past weekend - and he commented that he LOVED the image the GH2 produces - but everything above ISO 1000 was no good. So his observation confirms my findings.
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Old May 8th, 2012, 02:08 PM   #12
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Re: Knowing what the auto ISO is on

Yep, it's real and a little more complicated than I stated.
The firmware update and hacks can't fic it. It's just something to live with.

GH2 ISO noise bug at 320, 640, and 1250 - Personal View Talks

The GH2 ISO bug for 320 has been documented already: if you switch from ISO 250 to ISO 320, there's more noise than if you switch from ISO 400 to ISO 320. I have mapped the bug for ISO 640 and ISO 1250 as well. It seems that the bug is exhibited regardless of whether you record or not.

Switching to ISO 320: low noise from 400, 500, or sometimes 640; high noise from all others and from power off
Switching to ISO 640: low noise from 800, 1000, or 1250; high noise from all others and from power off
Switching to ISO 1250: low noise from 1600 or 2000; high noise from all others and from power off

I couldn't detect the bug when switching to any of the other ISO settings - if it's there, it's subtle. But for 320, 640, and 1250, it was unmistakable. Aside from the bug, I would say that none of the ISO levels seemed particularly more or less noisy than would be expected. I'd say to use whatever ISO level you need, being careful to avoid the bug.

Note that it is not sufficient to simply switch from any higher ISO to avoid the bug.

A good practice for ISO 320, 640, and 1250 would be to switch to the ISO setting 1/3 stop higher, and then back down. (i.e., 400 to 320, or 800 to 640, or 1600 to 1250).
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Old May 8th, 2012, 03:55 PM   #13
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Re: Knowing what the auto ISO is on

Wow...I just read that whole thread at personal-view.com. That is some heavy stuff! Thanks for the link Don, I'll have to keep that in mind when shooting.
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