color correction gels

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dv416

Well-known member
hey all

i am going to be buying some gels soon, but im a little confused about one thing.

my kit is all tungsten, 3200k, so i will need to get blue gels to correct it.

do all CTB gels adjust to 5600k? because i noticed there are varying degrees of ctb (1/4, 1/2, 3/4, etc). what do these #s indicate? blueness? opacity?

a brief explaination of ctb gels would be appreciated. couldnt find anything in the search.

thanks
 
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Yes indeed. If you put full ctb in front of a tungsten light, then your color temp would be as close to 5600k as possible, but keep in mind that all lights usually burn at slightly different temps even if they are the same make and model and with new bulbs. I know this because I work part time in a rental shop here in Montreal and part of my job is tracking the color temp difference of our HMI lamps as the bulbs age. So if you are using gels those numbers do refer to ratio of color correction, ie; half will give you a 50% increase in your temp and so on. The only really accurate way to know the color temp of a light is to use a colortemp meter, unless you have light meter that also displays color temp. Same goes for CTO. Also keep in mind that you are cutting the amount of light and the throw of the light when you use a gel, factor that in if you are shooting film. Hope this has helped.
 
I measured Lee CTBs with a shoulder mount camcorder (Sony DXC D30). Probably not as accurate as a color temp meter, but it gives you the ballpark.

The light I used was halogen:

Without gel: 3300K
With 1/2CTB: 4900K
With Full CTB: 7000K

This goes in line with my experience that a Full CTB will convert tungsten light to more than 5600K. It will fit the color temp of an overcast day, which is also around 6500-8000K. I didn't measure 3/4 CTB, but I guess you will get closest to 5600K with that.
 
so...if i'm using my indoor lights outside, i'm gonna want what? 3/4 ctb? full?

what do pros do in this situation, do they use lights that emit 5600k to begin with? or do they gel?
 
When you gel a tungsten light to daylight you loose about 2/3 of the power (the total efficiency drops from about 7% to 2-3%...). For that reason pros use HMIs or daylight fluorescents, where you get at least 5 times more light for the same amount of electricity. And no hassle with gels.
 
You'll never get a regular tungsten light to work well outside, just to have as much effect as a bounce board in direct sunlight, you're probably looking at 2000w without a gel, or 6000w with, a few feet away from your subject.

Full CTB is supposed to take 3200k to 5600k, if it's spec. If you use two 1/2 CTBs, they should do the same thing as a full CTB. When you need to be precise, and/or you're using sources that are not standard 3200k, you'll need to use the mired shift to calculate what to use.
David Mullen, ASC Explains
Mired Shift Calculator
 
Tungsten is all lights that are not HMI, fluorescent, sodium, mercury vapor, etc. etc.

Most worklights are tungsten or tungsten halogen.
 
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