GH13 Can't get rid of light flicker during night shoots - help!

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xocomil

Well-known member
Posted the other day but didn't get a response. Hopefully someone can help.

I've got a US-bought GH1 hacked. I have it set to PAL and shoot 25p (my client is PAL broadcaster).

Shooting at night I get flicker from floros/halogens. I've changed shutter from 1/50 to 1/60 to match the electricity here in Guatemala. But I still get serious flicker. I then tried 1/120 shutter (and every combination between 1/60 and 1/120) but the flicker persists.

Any thoughts GRATEFULLY accepted!
 
I would have thought 1/60 would have fixed the issues in 60Hz regions . Is it possible the "flicker" is from another underlying cause ? Exactly what are these lights ?

Theoretically this shouldn't make a difference, but if you shoot 24p native with 1/60 shutter do you still get the flicker ?
 
I believe with fluorescents there is not an exact hz but it fluctuates somewhat which is why it may be unavoidable in reality to get rid of flicker filming on the street. Also if there is any mixed lights
you may think none of the fluorescents should affect any shot, but in reality I think that even a glimmer from a far away different or fluctuating hz source could possibly cause a slight flicker to appear on footage. Night shooting is not predictable as far
as I know which is why most do it in a controlled area where they can turn off most all light sources and replace them with a set of their own consistent sources instead.

If you have no choice then I think that all you can do is what you have been doing, go through every shutter speed and setting and do 10 seconds of footage on each narrating over each what your settings are,
then see if any of them make any difference in your editor later. There is nothing more you can do then go through your whole settings, otherwise you have to change locations for good since I am presuming you can't
control the street lights themselves directly.

Update: Found these articles, it seems not only can the HZ fluctuate but the color as well. There seems to be contradiction in what different people say on these things as well so only your own testing will most
likely provide you with the best solution in a specific location.

http://lrt.sagepub.com/content/26/3/157.abstract

http://ezinearticles.com/?All-About-Fluorescent-Light-Flicker-in-Cameras!&id=3193172

http://therefractedlight.blogspot.com/2011/03/fluctuation-in-fluorescent-lighting.html
 
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Thanks guys.

PDR - yes I thought I should switch to NTSC framerates and see if the flickering persists. There's no other possible underlying cause.

Observe - interesting theory about the fluctuating frequency of fluorescent lights. As when I'm in these situations I can't control the street lights, nor can I switch locations, I'll have to go through all shutter speeds and test.
 
With multiple types of 60hz lighting sources, you may need to use a 1/30 second shutter speed at a 25p or 30p frame rate.
 
Cheers lpowell. Will throw 1/30 shutter into the mix.

And thanks for all the great patches!! You and Tester have turned this camera into a professional tool (albeit a somewhat fidgety one at times)!
 
I've been able to completely eliminate flisker before by going to 1/40th. Then you're still almost using correct shutter angle, but without flicker. It's worth a try.
 
How did this work? Asking since I'm going to the States in August and would need to know if 25 fps + 1/40 - 1/30 shutter is a workable set-up.
 
Well results weren't great. Least amount of flicker is with shutter set to 1/40th. It was slightly better than 1/30th. 1/50th is really bad, 1/60th slightly better .... and then it gets worse again.

Again, this is an NTSC GH13 shooting with lpowell's reliable playback hack (set to 25p in 50i stream - smooth settings).

Next step is to clear off my card and try setting output to NTSC framerates to see if it makes any difference (although that does nothing for me as I need to deliver in 50i).

Sorry Martti not to have more encouraging results (although your results might be completely different).
 
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xocomil said:
Next step is to clear off my card and try setting output to NTSC framerates to see if it makes any difference (although that does nothing for me as I need to deliver in 50i).
Click to expand...

It's worth a shot, people still use "PAL speed up." BBC does this all the time with film material

In post, on technique people use is temporal smoothers to improve the flicker from fluro lights
 
xocomil said:
Can you elaborate? I use FCP. Many thanks for taking an interest!
Click to expand...

Sorry, I only know of Windows workflows for this; I don't know what the equivalent filters would be called in FCP. But I posted some examples in another post for LED flicker; it basically involves frame averaging filters.

http://www.dvxuser.com/V6/showthrea...g-LED-lights&p=2335735&viewfull=1#post2335735

On low motion scenes, you can get good results, but on scenes with lots of movement, there can be quite a bit of detail loss because of the smoothing. It's really only a "band aid" solution that can salvage some material - It would be better to try to get a synchronized frequency or fix it with in camera settings if possible. There is a plugin for AE that does something similar from Revision:FX that is included with DE:Noise called frame averager.
 
xocomil said:
Shooting at night I get flicker from floros/halogens. I've changed shutter from 1/50 to 1/60 to match the electricity here in Guatemala. But I still get serious flicker. I then tried 1/120 shutter (and every combination between 1/60 and 1/120) but the flicker persists.
Click to expand...

Yeah, it probably will persist. A couple of reasons why. First, your camera is not in sync with the electrical grid -- you start filming at some random part of the 60Hz signal, so no telling when your exposures take place. Second, the power companies tend to manipulate the actual frequency during the day. Sounds crazy, I know, but by selectively slowing down and speeding up frequency they can improve their efficiency. As long as the total number of cycles during the day is fixed (60 x 60 x 60 x 24), most people won't know and their clocks will be right. But it's not at all unusual for a power company to be putting out 59.2 Hz power.

I'm just sayin' that it's really unlikely that your camera will be in sync with the local power grid. And therefore it is equally unlikely that you'll get flicker-free video if you use magnetic ballast fluoros that use the power grid for frequency. This is one reason why professional cine lighting is nice -- electronic ballasts with very high frequencies basically eliminate any possibility of flicker in your vids, regardless of your shutter speed / frame rate.
 
Thanks Bruce for your input. What I don't understand is how others can shoot under streetlights (with no extra lighting equipment) and not get the flicker. I presume this problem should effect all videocameras no?
 
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