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Sony A7S - LED light banding and flickering?

DSLR Flicker Banding Video

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#1 CRISTINA WOLF

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Posted 27 April 2016 - 10:31 AM

Hello-

 

I am shooting a film and I planned to use the Sony A7s and these TV simulation LED flickering lights. But the lights cause banding and video flicker. 

 

 

Is there a way to get a  "clear scan" on the A7S camera?

 

Thanks!

 

 

The light: 

http://www.amazon.co...61771088&sr=8-1


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#2 JD Hartman

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Posted 27 April 2016 - 10:43 AM

Rent a Magic Gadgets flicker box and use a couple of colored Tungsten bubs.


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#3 Satsuki Murashige

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Posted 28 April 2016 - 12:39 AM

You can try setting the shutter speed to 1/60 or whatever power frequency the light operates on, but if that doesn't work then I don't think it will be possible to avoid banding. As JD suggests, the simplest solution is to just use tungsten lights or Kino Flos.

One solution I have used in the past that works well is to light with a soft source and wave your hands slowly in front of the light. I used a Kino Flo Image 80 behind a 12x12 diffusion frame to simulate a flickering movie screen with good results. Two of us waved pillows at irregular intervals between the light and the frame. Since a TV screen is much smaller, you could probably just use a 2x2 Kino or a Diva and a 4x4 diffusion frame to get a similar result.

Another solution I have used is 4x Rosco Litepads velcro'd to a piece of silver showcard. Each 3x6" Pad was gelled with a different color and ganged to a Rosco Litepad 2-channel DMX dimmer. We didn't use the dimming function, but just switched the channels on and off are irregular intervals. This is good if you need a reflection of the screen off of a dark satin-finish surface like a door or wall.

Finally, a more stylized but very simple approach is to plug a dimmer into a tungsten fresnel and dim the gag light up and down by hand. I did this once when shooting an old 1950s TV set prop with the tube removed. I put a 150w fresnel inside the tv housing itself since the back of the TV set was in the shot. It worked well since the film was black and white and stylized to look like 1950s studio era photography anyway. You could see the light flickering out of the air vents in the back of the TV which was a neat effect.
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#4 JD Hartman

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Posted 28 April 2016 - 06:20 AM

You can try setting the shutter speed to 1/60 or whatever power frequency the light operates on, but if that doesn't work then I don't think it will be possible to avoid banding. As JD suggests, the simplest solution is to just use tungsten lights or Kino Flos.

One solution I have used in the past that works well is to light with a soft source and wave your hands slowly in front of the light. I used a Kino Flo Image 80 behind a 12x12 diffusion frame to simulate a flickering movie screen with good results. Two of us waved pillows at irregular intervals between the light and the frame. Since a TV screen is much smaller, you could probably just use a 2x2 Kino or a Diva and a 4x4 diffusion frame to get a similar result.

Another solution I have used is 4x Rosco Litepads velcro'd to a piece of silver showcard. Each 3x6" Pad was gelled with a different color and ganged to a Rosco Litepad 2-channel DMX dimmer. We didn't use the dimming function, but just switched the channels on and off are irregular intervals. This is good if you need a reflection of the screen off of a dark satin-finish surface like a door or wall.

Finally, a more stylized but very simple approach is to plug a dimmer into a tungsten fresnel and dim the gag light up and down by hand. I did this once when shooting an old 1950s TV set prop with the tube removed. I put a 150w fresnel inside the tv housing itself since the back of the TV set was in the shot. It worked well since the film was black and white and stylized to look like 1950s studio era photography anyway. You could see the light flickering out of the air vents in the back of the TV which was a neat effect.

 

I think the frequency would only be 60Hz if the TV stimulator had a linear power supply,  Somewhat unlikely in small electronic gadget probably powered by a wall wart and a high frequency switching power supply.

 

Somewhat or totally OT, couldn't you just have a flickering TV in the background?  I recall doing this once, but can't remember the details.  Then again, I'm no camera guy.


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#5 Satsuki Murashige

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Posted 28 April 2016 - 10:15 PM

I think the frequency would only be 60Hz if the TV stimulator had a linear power supply,  Somewhat unlikely in small electronic gadget probably powered by a wall wart and a high frequency switching power supply.

Yes, that's true. The original poster could try cycling through all of the available shutter speeds but I don't think the control on the A7S is fine enough to match frequency.

Somewhat or totally OT, couldn't you just have a flickering TV in the background?

Yes that could work as well, though you will run into the same frequency banding issues with LCD, LED, or Plasma TVs.

I recall one commercial job as a young AC where the director/DP/production company owner asked me to shoot a quick pickup night interior scene of a young couple in front of a TV.

We had already been shooting for 18 hours that day, after a 5hr turn-around, pre-dawn flight from SF to LA, shooting desert highway shots out in Lancaster, flying back to SF, and driving back to the production office with all the gear. Full Mitchell sticks, babies, 2575, Angenieux HR, Red One. Just me and him, and a PA/driver in LA. Totally insane.

Being completely brain dead, I proceeded to set up lights and a flicker gag and shot the scene. Brought the media over to the edit bay where my boss was supervising another edit. He took one look and called the actors back in. We re-shot it immediately with no lights and real tv flicker by cranking the gain and dropping the shutter speed. So sometimes the simplest method is best. I didn't think my effort was that bad at the time, but clearly I still had a lot to learn.
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#6 John Miguel King

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Posted 29 April 2016 - 02:44 AM

The A7s has very serious rolling shutter issues. It's even worst than the 5d. Bang a long lens (say an 80mm) and rock the camera ever so slightly. You'll see how jello everything turns.

This affects banding, as it's just another symptom of the same disease.

There's also the issue of Pulse Width Modulation being the de facto dimming approach with leds. Cheap dimmers work at such low frequencies that banding will happen regardless. In order to eliminate PWM as one of the causes the dimmer should be working at 1 khz or faster.

Kinos, for example, work at 10 khz.

The correct approach, if going led, would be using an RGB led matrix through an Arduino controller. This way you can create any color effect you wish whilst working at a very high frequency.


Edited by John Miguel King, 29 April 2016 - 02:47 AM.

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#7 Landon D. Parks

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Posted 02 May 2016 - 10:48 PM

Which is a major disadvantage of large sensors with large numbers of pixels - slow readout, resulting in terrible rolling shutter. FF DSLR's are the biggest culprit. While the A7S may be good for low light, it isn't that great for much else. 


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