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-   -   what ctb gels to use? (https://www.dvinfo.net/forum/photon-management/31620-what-ctb-gels-use.html)

Zach Schuyler September 9th, 2004 05:12 AM

what ctb gels to use?
 
I am having to light a hallway where daylight is pouring in from from windows on on side. I would like to use CTB gels on my lights but don't which ones to buy. Full, 3/4, half, 1/4 or 1/8. The amount of light that is coming is strong and the windows are huge, so covering them with CTO gels is out of the question. Any help would be appreciated.

I am using quartz halogen (worklights) which I heard registers at about 3000 degress Kelvin, just slightly below 3200.

In a description I read , it said that Full CTB gel brings 3200 to 5500, but 1/8 brings 3300 to 5500 which I don't undestand. How could a lower CTB gels bring a higher color temperature to 5500?

Barry Green September 9th, 2004 11:14 AM

They don't. The strength of the gel (i.e., 1/4, or 1/8, etc) determines how much correction it does. Full CTB is probably what you want, converting your 3000k lights to approximately 5500k.

Daylight isn't always 5500k, it varies widely depending on the time of day, whether it's overcast, etc. Daylight can register at over 10,000k... but if you gel your lights with full CTB you'll be in the ballpark.

Charles Papert September 9th, 2004 02:04 PM

Barry's advice is solid. But the question may lie in what look you intend to create visually with the scene. Full correction on the lights and white balancing to daylight will give you a "normal" color rendition. Considering that you are using worklights in a situation where the ambient light levels are high (and your shooting stop will be adjusted accordingly), adding full blue may reduce your lights to a mere whisper. If you were willing (and felt it was appropriate to do so), you could half-correct the lights using 1/2 CTB then white balance under that light. The daylight will be a bit on the cool side; more white than blue, really. And you will realize a bit more output from your worklights this way. I did just this on a short recently (watch it here: the second scene, walking through the office, is just as I described above. You can even see the warmth of the uncorrected 3100K ceiling spots as they walk through the shot.

Mixing color temperatures is not only "allowed", it's a pretty contemporary look. You can even go radical by adding CTO to your worklights and white balancing to that, and allowing your daylight ambient to go REALLY blue--interesting look! As always, experimentation is best, done ahead of time.

Richard Alvarez September 9th, 2004 03:08 PM

CHARLES!

Way to wail on the sax man!! What a nice piece, well crafted. What was it shot on?

Charles Papert September 9th, 2004 07:52 PM

Thanks--here's the thread that should answer all.

Bill Hamell September 9th, 2004 09:29 PM

Re: what ctb gels to use?
 
<<<-- Originally posted by Zach Schuyler : I am having to light a hallway where daylight is pouring in from from windows on on side. I would like to use CTB gels on my lights but don't which ones to buy. Full, 3/4, half, 1/4 or 1/8. -->>>

This should help it is from the Rosco site.
Other brands of gel should be of equal values.

If your lights are 3000K than adjust the figures as needed.
Also remember you can combine gels to get the value you need.

Mr. Bill

Cinegel #3202: Full Blue (CTB)
Standard Tungsten to daylight correction. Boosts 3200K to nominal 5500K daylight. Deep-dyed base. (Mired shift = -131, Trans.= 36%, -1.5s).

Cinegel #3203: Three-Quarter Blue (3/4 CTB)
Boosts 3200K sources to 4700K. Used when a partial conversion is desired, or when daylight is below 5000K. Deep-dyed base. (Mired shift = -100, Trans.= 41%, -1.3s).

Cinegel #3204: Half Blue (1/2 CTB)
Boosts 3200K sources to 4100K. A partial comversion to compensate for varying daylight conditions and voltage reduction, or to boost aging HMI lamps and yellowed soft lights. Deep-dyed base. (Mired shift = -68, Trans.= 52%, -0.9s).

Cinegel #3206: Third Blue (1/3 CTB)
Boosts 3200K sources to 3800K. A partial conversion to compensate for varying daylight conditions and voltage reduction, or to boost aging HMI lamps and yellowed soft lights. Deep-dyed base. (Mired shift = -49, Trans.= 64%, -0.6s).

Cinegel #3208: Quarter Blue (1/4 CTB)
Boosts 3200K sources to 3500K. A partial conversion to compensate for varying daylight conditions and voltage reduction, or to boost aging HMI lamps or household incandescant sources. Deep-dyed base. (Mired shift = -30, Trans.= 74%, -0.4s).

Cinegel #3216: Eighth Blue (1/8 CTB)
Boosts 3200K sources to 3300K. A partial conversion to compensate for varying daylight conditions and voltage reduction, or to boost aging HMI lamps or household incandescant sources. Deep-dyed base. (Mired shift = -12, Trans.= 81%, -0.3s).

Cinegel #3220: Double Blue (2 x CTB)
Boosts 2800K sources to 10,000K. An over correction filter designed for special applications. Deep-dyed base. (Mired shift = -260, Trans.= 10%, -3.3s).

Stephen Schleicher September 10th, 2004 10:29 AM

Out of curiousity, if your "set" has huge windows with light streaming in, do you really need additional light? Could you achieve your lighting set up with bounce cards?

Just a suggestion

Cheers

Charles Papert September 10th, 2004 04:32 PM

Oh yeah, I meant to say that but I forgot, thanks Stephen!

Jacques Mersereau September 11th, 2004 09:58 AM

Hold on here. From what Zach says the incoming light is strong and
coming from HUGE windows.

If you gel your 500W work lights with full color correction gel (like Lee 201)
they turn into 75-100W. That isn't going to keep with with
direct sunlight. NO WAY.

I would strongly suggest getting some netting or screen to
knock down the strength of that direct sun light. Then you
might have a chance. Bouncing the sunlight is also a good idea,
but never seems to keep up unless the card is
right next to the talent and then they are blinded.

I would look for some netting or screen and/or shoot early/late in the day
when you don't have to deal with harsh direct sunlight.

Charles Papert September 11th, 2004 10:52 AM

Jacques, I believe I addressed the effects of the gel on the output of the worklights?

And Zach suggested that gelling the windows is "out of the question", so we can assume the same for the use of the nets.

I think that your last suggestion of shooting when the light is purely ambient (no direct sunlight) will achieve the best results, and won't require any additional fill.

Zach Schuyler September 15th, 2004 03:33 PM

what I ended up doing
 
We ended up shooting later in the day when there was no direct sunlight coming in through the windows, which knocked down on the shadows against the wall. I did use a 3/4 CTB get when the actors got closer to my lights. The resulting video ended up looking good.


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