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ARRI 300 and CTB problem


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#1 julien doumenjou

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Posted 19 April 2010 - 11:45 AM

Hi,

just shoot a scene in an office (med-shot) using daylight from window and 2 ARRI 300. There was enough light until I put the CTB on the ARRI (of course I had to do it for color balance). Is it my imagination or Arri 300 is really low using with CTB ? Unless used for close up ?
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#2 Jeff Kolada

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Posted 19 April 2010 - 12:16 PM

full CTB takes a full stop of light away from anything you put it in front of. So usually if you're going to CTB a light, it should be twice as bright as you would have it without a filter, or closer to the subject.

I am assuming you're using full CTB.

FullCTB: 1 Stop Loss
HalfCTB: 3/4 Stop Loss
QrtrCTB: 1/2 Stop Loss
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#3 Chris Keth

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Posted 19 April 2010 - 12:48 PM

full CTB takes a full stop of light away from anything you put it in front of. So usually if you're going to CTB a light, it should be twice as bright as you would have it without a filter, or closer to the subject.

I am assuming you're using full CTB.

FullCTB: 1 Stop Loss
HalfCTB: 3/4 Stop Loss
QrtrCTB: 1/2 Stop Loss


Full takes 1-2\3 stops. It felt like the light was low because it was! Your 300W was working as only about a 120 watt fresnel.
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#4 julien doumenjou

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Posted 19 April 2010 - 01:07 PM

full CTB takes a full stop of light away from anything you put it in front of. So usually if you're going to CTB a light, it should be twice as bright as you would have it without a filter, or closer to the subject.


So I should have used a 650W instead of a 300 ?
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#5 JD Hartman

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Posted 19 April 2010 - 02:05 PM

1/2 CTB would bring the color temp close enough, full CTB actually over-corrects.
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#6 Brian Drysdale

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Posted 19 April 2010 - 04:06 PM

1/2 CTB would bring the color temp close enough, full CTB actually over-corrects.


Full CTB is, perhaps a little under a full correction to daylight, but close enough. 1/2 CTB is no where near a full correction to daylight. I know people use it, but it's a compromise for light output.

On the over correction front, it's full CTO that over corrects converting daylight to tungsten.
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#7 Chris Keth

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Posted 19 April 2010 - 04:58 PM

So I should have used a 650W instead of a 300 ?


If you wanted similar output to the bare 300W, I would have used a baby and then had room to scrim it down if need be.
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