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Canon XH Series HDV Camcorders
Canon XH G1S / G1 (with SDI), Canon XH A1S / A1 (without SDI).


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Old March 19th, 2007, 11:06 AM   #1
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Exposure weirdness

There has been criticism before about the way Canon HDV cameras handle highlights and I have to say, based on my own tests, these comments are well founded.

From what I have seen so far, there is nothing eloquent about how the XHA1 handles highlights, even with the knee set to low. It goes from exposed to blown out in a single step.

What is a little confounding is that I always use zebra stripes to judge exposure and I've usually been able to record what I am seeing exactly how I want it.

I currently have the zebras set to 100, just like I had on my DVX and I am very careful about not letting certain areas clip. When I look at high contrast areas of my shots (for example, a tree on the horizon with a bright sky behind), I am seeing lots of clipping. This was clearly not happening when I was looking through the viewfinder, no zebras, good exposure. This should not be happening so I am thinking I will need to bump down the zebras to 90 or even 80 which seems weird to me.

Has anyone encountered this strange behavior?
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Old March 19th, 2007, 11:43 AM   #2
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If you shoot with zebras at 100 percent, the only time you should see the zebras would be on something white in the direct light part of the frame. Broadcast cameras I've used have always set zebras at 75-80% for normal use, and that's what I use on all cameras with no problem. With zebras at 80%, you see them on a medium sort of thing, like caucasian skin tones, light blue shirt, etc., or a gray card if you want that precision, then back off a bit, and you're usually there. If you're getting zebras at 100% on average reflectance parts of your frame, then you're overexposing.
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Old March 19th, 2007, 11:46 AM   #3
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OKay Bill, thanks for the info. Weird that I didn't have the same problem with the DVX. I'll make the adjustment based on your recommendation.
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Old March 19th, 2007, 12:02 PM   #4
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As a matter of interest how are you determining whether they are blown out or not? The reason I ask is that when using Vegas I've noticed that there's a lot of info above 100IRE (Using the Waveform Monitor) and if I pull that back down I get quite some detail back.

This may have nothing to do with it - I just noticed I had the issue with a shot with lots of sky in it and by using curves was able to get some detail back...but I'm not a professional shooter, yet, I know more about the post processing side. I've come from DSLR background where you 'shoot to the right' and pull the info back in using the raw data afterwards.

...maybe I'm on the wrong track here.
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Old March 19th, 2007, 12:05 PM   #5
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Simon, I noticed it because there were chunks of branches missing. Their ends were detached from the main tree because the intensity of the sky had eaten them up. There is no rescuing this information because it was never recorded to tape.

It's rare when you can get any information from an overexposed area like this.
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Old March 19th, 2007, 12:31 PM   #6
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I've not noticed this at all with my XH-A1.

Can you post a screen grab please and I'll try and replicate.

Cheers

TT

There are some electricity pylons on the horizon against a bright sky. My zebras are on 100 and even when the sky is uniformly registering at 100% the pylons are still sharp. It is not until I over-expose by about 2 stops that the detail is lost as you'd expect.

In your shot are you shooting into the sun causing the tree to be in silhouette?

I've always thought the XH-A1 handled highlights pretty well. As good as any other current compact HD camera.

Last edited by Tony Tremble; March 19th, 2007 at 12:58 PM. Reason: Adding my own quick obs
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Old March 19th, 2007, 12:57 PM   #7
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Tony, I think the problem has been identified. I just had the zebras set too high. A simple adjustment should fix the problem. I'll let you know.

Thanks
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Old March 19th, 2007, 01:23 PM   #8
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Working with zebras set 100% is risky by definition. Even without reaching the limit, brightness levels at some spots in conjunction with all factors at play (starting with haze and air quality, through lens properties, ending with electronic path and codec limitations) may cause problems that you have noticed.

To really figure the difference between A1 and DVX behavior you would need to compare then side by side in the same conditions. I don't think there's much of difference here.

All cameras, film and digital, suffer this way because dynamic range of typical daytime scenery exceeds their capacity. It's only a question of pushing them far enough. The other reason is limited resolution of zebra and sometimes one may not be aware that clipping actually occurred. That's why most people prefer to work with zebras set less than 90%.
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Old March 19th, 2007, 01:24 PM   #9
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Hi Steven,

I noticed that too, early on when I got the camera and set the zebra's
to 80%, that helped a lot.

good luck with it,

David
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Old March 19th, 2007, 01:30 PM   #10
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Okay, thanks everyone...I'll do some further testing using 80% zebras but I'm pretty sure that will work.
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Old March 19th, 2007, 02:02 PM   #11
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Oops, some server or connection problem occurred and my previous post got doubled.

Chris - could you do a favor to remove this one? Thank you!
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Old March 19th, 2007, 04:22 PM   #12
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I don't understand why 100 zebras would cause the problem. 100=100 as far as I can see.

I've not had a problem with Canon Zebras set at 100.

I don't understand....

TT
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Old March 19th, 2007, 04:27 PM   #13
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Okay so here's the deal.

I realized when I looked at my settings on the camera that my zebras somehow got turned off so I was assuming they were on and looking to see them when I was shooting this morning. I assumed I was within exposure range but was not.

So that's my embarrassing confession :)

Nonetheless, the Canon cameras do blow out very quickly even with a low knee setting and it will suit me better to have an "early warning system" by putting the zebras on probably 85% or 90%...
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Old March 19th, 2007, 09:31 PM   #14
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The stinker with the A1 is that if you happen to toggle peaking on and forget about it, you've lost your zebras. It would be really nice if you could use peaking and focus assist while the cam was recording...and still keep the zebras up!
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Old March 19th, 2007, 10:03 PM   #15
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Steven, I've noticed it too, the A1 is quick to blow out, particularly as compared to the dvx. I keep peaking on due to the weak LCD, and I miss the zebras. If you're using the lcd, have you knocked down the brightness? It helps somewhat.
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