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Author Topic: Flickering light in my studio outputs  (Read 7504 times)

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« on: September 08, 2015, 20:39 »
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After months of traveling for fun and work I was finally able to use my GH4 in the studio.  I have two LED 1200 lumen continuous lights and a couple of smaller Fiilex spot lights.  I was shooting some food in bowl and had both LED lights set up fairly close to the food and a spot light on the front of the food.  This was the first time I've had a chance to shoot the GH4 in the studio but I have used my Nikons a lot.  When I was shooting, the light in the camera flickered making the footage useless but the light on the subject was smooth and consistent.  I thought maybe it was the frequency settings in the camera. I was shooting Cine V mode but the frequency was set to 59.9 hertz. Cinema modes usually require 24 hertz, so I have read.  So I switched the frequency on the GH4 to 24 hertz and the flickering stopped, but the output of rotating food was jittery. So not useful.  Cine V is very sharp on video output but if I put the GH4 in normal mode the video is horribly soft (I have no clue as to why). On normal mode I would shoot in NTSC hertz 59.9 if I could get sharp output. 

Does anyone have any guidance they can offer that could solve this issue?


wds

« Reply #1 on: September 08, 2015, 21:25 »
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- What do mean by "the light in the camera"?
- I would guess that any flickering was due to the LED lights having an issue. What model make are they?

« Reply #2 on: September 08, 2015, 22:27 »
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- What do mean by "the light in the camera"?
- I would guess that any flickering was due to the LED lights having an issue. What model make are they?

While recording you could see flickering lightng in the camera monitor and when i put it in final cut pro. So It is from the camera, that much i know. I am shooting with ledgo 1200 LS panel lights.

« Reply #3 on: September 08, 2015, 22:40 »
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There is actually an adjustment on the GH4.

From the Panasonic website. Menu page 4/6 of the Movie menu on the camera. Must be in creative movie mode M.

What is the Synchro Scan? - DMC-GH4
 
Synchro scan automatically reduces flicker under fluorescent light etc. with finer adjustment than conventional flicker reduction function, It can be used in M-mode video recording

http://www.manualslib.com/manual/696100/Panasonic-Dmc-Gh4.html?page=218
« Last Edit: September 08, 2015, 22:46 by Zeus »

« Reply #4 on: September 09, 2015, 03:09 »
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Have you determined which lights caused the flickering?

« Reply #5 on: September 09, 2015, 04:00 »
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Just a couple of thoughts.
Some LED lights "flicker" on and off rapidly. I've got a head torch that makes the fans in the computer appear to be running slowly from the strobe effect.
If you are shooting NTSC 59.9 Hz, what is the mains frequency where you are? If it's 60 Hz that could give all sorts of weird "interference" type flicker between the two frequencies I'd have thought.

« Reply #6 on: September 09, 2015, 06:06 »
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Yes some LED are dimmed by PWM, short burst of current instead of less current. Most studio LEDs don't do this because of the flickering.

« Reply #7 on: September 09, 2015, 07:23 »
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Have you determined which lights caused the flickering?

I have not. I am going to try a couple of things Zeus posted. As usual I'm sure there is a solution, it's just a learning experience. I assume based on my reading online that if I had set the shutter speed at 200, for example, I would get flicker.....as opposed to setting it at 50 (24 hz) or 60 (59.9 hz). 

Diffydave, very interesting you say that. It was my first thought. I could not see the flicker on the subject but it was very noticeable in the GH4 monitor.  And it wasn't patronized, more random.  2-3 seconds of good light and them flicker like a haunted house. 

wds

« Reply #8 on: September 09, 2015, 07:50 »
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It's gotta be the LED lights "flickering" beating against the frame rate of the video. If the LEDs and the camera framing "phase" happen to be insync, flickering will be minimal, but as they drift apart, flickering gets worse. Try going to all incandescent lighting.

« Reply #9 on: September 09, 2015, 07:52 »
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It's gotta be the LED lights "flickering" beating against the frame rate of the video. If the LEDs and the camera framing "phase" happen to be insync, flickering will be minimal, but as they drift apart, flickering gets worse. Try going to all incandescent lighting.

Interesting. I'm heading to Sammy's camera today to chat with their video guys. I'll bring this up. Thanks for the tip.

« Reply #10 on: September 09, 2015, 08:57 »
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You can also change the frequency refresh rate of the monitor.

« Reply #11 on: September 09, 2015, 09:14 »
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Quote
So I switched the frequency on the GH4 to 24 hertz and the flickering stopped, but the output of rotating food was jittery.

Lights aside can you explain the above in more detail?24p (and not 23.98 i suppose) with 1/48 shutter is what you used?Same setting in your nle?How do you mean jittery?

« Reply #12 on: September 09, 2015, 09:26 »
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Quote
So I switched the frequency on the GH4 to 24 hertz and the flickering stopped, but the output of rotating food was jittery.

Lights aside can you explain the above in more detail?24p (and not 23.98 i suppose) with 1/48 shutter is what you used?Same setting in your nle?How do you mean jittery?
24P is known for jutter. Do a Google search and there is lot written about this. Plus for some reason the GH4 has a greater propensity for rolling shutter at 24P.

« Reply #13 on: September 09, 2015, 09:35 »
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Quote
So I switched the frequency on the GH4 to 24 hertz and the flickering stopped, but the output of rotating food was jittery.

Lights aside can you explain the above in more detail?24p (and not 23.98 i suppose) with 1/48 shutter is what you used?Same setting in your nle?How do you mean jittery?
24P is known for jutter. Do a Google search and there is lot written about this. Plus for some reason the GH4 has a greater propensity for rolling shutter at 24P.

It is as jittery as 25p in that regard.Depends on what you film and the motion,but i asked because i suspected wrong shutter settings.

« Reply #14 on: September 09, 2015, 09:56 »
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Quote
So I switched the frequency on the GH4 to 24 hertz and the flickering stopped, but the output of rotating food was jittery.

Lights aside can you explain the above in more detail?24p (and not 23.98 i suppose) with 1/48 shutter is what you used?Same setting in your nle?How do you mean jittery?
24P is known for jutter. Do a Google search and there is lot written about this. Plus for some reason the GH4 has a greater propensity for rolling shutter at 24P.

It is as jittery as 25p in that regard.Depends on what you film and the motion,but i asked because i suspected wrong shutter settings.
There is the high shutter speed staccato look. But my guess is you know what that's like. Then there is the random lag that looks awful but you can't do much about look. I've torn my hair out on these many times but if you watch movies, they are very common with faster pans.

« Reply #15 on: September 09, 2015, 10:08 »
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At 24p the video is jittery but the light is smooth. At 29.9 frame rate the video is smooth but the lighting in the video flickers randomly. I am going to test shutter speed based on the info zeus provided in a few days. Hopefully that respoves things but we will see. I will try to post a link to my drop box so you can see what it looks like.

« Reply #16 on: September 09, 2015, 10:20 »
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At 24p the video is jittery but the light is smooth. At 29.9 frame rate the video is smooth but the lighting in the video flickers randomly. I am going to test shutter speed based on the info zeus provided in a few days. Hopefully that respoves things but we will see. I will try to post a link to my drop box so you can see what it looks like.
Mantis, search on Beat Frequencies and you'll see plenty written on the physics of what's happening. The clock in the camera is slightly different to the frequency of the line voltage, which determines the pulse rate of the LED lights.

Benozaur

« Reply #17 on: September 09, 2015, 11:49 »
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The theory behind this is quite simple. If you are living in the USA you will probably be powering your lights using mains electricity at 60Hz. If you are living in the UK, then its 50Hz. Hence USA had the NTSC video system at 30 frames per second and the UK had PAL at 25 frames per second.
60Hz at 30fps and 50Hz at 25fps, see the relationship?

So if you are experiencing flicker I suggest you set your shutter speed to a multiple of however many Hz you're using to power your lights.

I live in Europe, PAL region, so I film at 25fps and a shutter speed of 50, 100, 200, etc...

« Reply #18 on: September 09, 2015, 12:54 »
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There are few software options you could use to fix your problem. Something like this, for example: http://www.digitalanarchy.com/Flicker/main.html
Their examples look good, but I find them a little pricey

« Reply #19 on: September 09, 2015, 13:17 »
+1
The theory behind this is quite simple. If you are living in the USA you will probably be powering your lights using mains electricity at 60Hz. If you are living in the UK, then its 50Hz. Hence USA had the NTSC video system at 30 frames per second and the UK had PAL at 25 frames per second.
60Hz at 30fps and 50Hz at 25fps, see the relationship?

So if you are experiencing flicker I suggest you set your shutter speed to a multiple of however many Hz you're using to power your lights.

I live in Europe, PAL region, so I film at 25fps and a shutter speed of 50, 100, 200, etc...
I believe it's exactly this that causes the problem. The fact that the camera record frequency is very close to the light strobing (i.e. flicker rate) frequency. It's the slight variation of the two that gives a BEAT or strobing effect.

Benozaur

« Reply #20 on: September 11, 2015, 05:17 »
+1

Thats correct, any variation gives a flickering or even strobe effect. The trick is to get the two in sync...


 

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