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Interference Pattern with 7D?

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Jonathan Ziegler
Interference Pattern with 7D?
on Mar 8, 2010 at 7:23:45 pm

So I'm seeing something I've not seen for a while: what looks like an interference pattern.

We shot with a 7D using available light which was fluorescent light (your standard, everyday overhead type). In the footage with this lighting, I'm seeing a very subtle interference pattern against the back wall in the shot - it's a sort of subtle banding of dark and light that slowly creeps up. Shot f5.6, ISO 1600, shutter 1/50, lens 60mm, 24p.

Anyone else seeing this and will a 1/60 shutter or a longer shutter help this?

It's too late to pickup any more footage and I'll have to stick with it and it's so subtle, most won't see it (I missed it on the first 2 takes) and it's not there long enough to catch it unless you're looking for it. I'm guessing this is a sort of rolling shutter issue coupled with the subtle strobe of fluorescent light - like banding of a TV in similar situations.

Sorry, can't post the footage without getting in trouble. Anyone know of a fix in FCP?

Jonathan Ziegler
http://www.electrictiger.com/
520-360-8293


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Robbie Carman
Re: Interference Pattern with 7D?
on Mar 8, 2010 at 11:45:00 pm

sounds like power cycle flicker to me from the lights. Although in theory those lights should cycle at 60hz in reality not always the case. I was recently grading some concert footage that was light under house lights ( low quality HMI's maybe a diva mixed in) and there was noticeable flicker even though the team was shooting at 1/60th to match that power cycle

Robbie Carman
----------------
Colorist and Author
Check out my new Books:
Video Made on a Mac
Apple Pro Training Series DVDSP
From Still To Motion





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Jonathan Ziegler
Re: Interference Pattern with 7D?
on Mar 9, 2010 at 12:15:22 am

Yeah, after your post, I looked at mine - we shot at 1/50. Answers my question. I'll know better next time. Thanks!

Jonathan Ziegler
http://www.electrictiger.com/
520-360-8293


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Robbie Carman
Re: Interference Pattern with 7D?
on Mar 9, 2010 at 1:01:22 am

yeah 1/50th which shooting 24 is what you'd normally want sometimes you'll have to break the rules on situations like fluorescent consumer lighting

Robbie Carman
----------------
Colorist and Author
Check out my new Books:
Video Made on a Mac
Apple Pro Training Series DVDSP
From Still To Motion





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Norman Pogson
Re: Interference Pattern with 7D?
on Mar 9, 2010 at 12:58:00 pm

I even had it with shooting close ups of LED Christmas lights outdoors, I could see the cycling on the 7D lcd panel, I adjusted the shutter until it went away.

My Canon 7D Blog


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Jonathan Ziegler
Re: Interference Pattern with 7D?
on Mar 9, 2010 at 3:07:09 pm

My camera guy was saying something about it, but seemed to think it would work. I'm thinking maybe a 1/30 shutter should be good for the next time. It was awfully low light after all.

Jonathan Ziegler
http://www.electrictiger.com/
520-360-8293


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Uli Plank
Re: Interference Pattern with 7D?
on Mar 10, 2010 at 7:08:01 am

While AFAIK there is no filter for FCP, we made use of the free deflicker filter for virtual dub on footage we shot under available light (most flourescent) with a European camera in Brazil.

Hope this helps,

Uli

Director of the Institute of Media Research (IMF) at Braunschweig University of Arts


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