Differences between gels?

J

Jacoolh

Member
Hi everyone,

I am an aspiring DP with most of the camera side sorted, now I really want to brush up on lighting techniques as I feel I don't have enough at the moment. Just need clarification as to what gels are what? I only ask as I have heard there two separate types, one for colour correction and one to maybe just slightly change the temp? As I said this is why I need some clarity on the matter.

Anyone have any links to help me? I couldn't find one in the lighting stickies ;)

Cheers.
 
hi jacoolh,

colour correction gels come in lots of varieties, the most common are "colour temperature blue" CTB and "colour temperature orange" CTO.
CTB converts tungsten light to daylight.
CTO converts daylight to tungsten

full CTB converts 3200k to 5700k
3/4 CTB convert 3200k to 5000k
1/2 CTB converts 3200k to 4300k
1/4 CTB converts 3200k to 3600k

full CTO converts 5600k to 3200k
1/2 CTO converts 5600k to 3800k
1/4 CTO converts 5600k to 4600k

figures based on lee filters

there are hundreds of gels available for light control in all sorts of combinations.

check out the lee filters website and get yourself a filter swatch book, the filter companies
usually give them away.

cheers
 
You've got some gels which are scientifically engineered to change the color temperature of light so that lights of different temperatures will match each other. These are of precise color and weight. These are CTO and CTB gels, minus green, plus green, etc.

Then you've got gels which just make pretty colors (or not, if you like). These are called "party gels."
 
Simplifying things a bit... look at the light sources you shoot under and the lights you own/rent.

If you have a variety of tungsten and daylight sources, you may need to match them;
You may need to match daylight to your lights;
You may need to match lights to, say, warm sunset light or blue-gray shade.

So, pick up the appropriate gels for doing that. In my case, I have a lot of full and half CTB and some 1/4 as I generally shoot daylight and often have to match fresnels to flos.

I also like to take a sharpie and mark my CTBs in the corners - if I cut them up, I'll know what the pieces are (this because I have a huge roll of "colors" and don't want to confuse the blues). In the dark, it can be hard to tell a 1/2 from a full CTB in a hurry.

Garish colored gels - buy them as needed for special projects. Keep more subtle colors on hand that will fine tune your looks. In my case, straws and 1/4 CTB are real go-to's... I've used light rose gels on female talent at times. If you shoot a lot of horror/sci fi, some greens for that fluoro look may be what you need.
 
Michael Carter said:
I also like to take a sharpie and mark my CTBs in the corners - if I cut them up, I'll know what the pieces are (this because I have a huge roll of "colors" and don't want to confuse the blues). In the dark, it can be hard to tell a 1/2 from a full CTB in a hurry.
Click to expand...
Yes, important and you can just use shorthand. You know the gel is blue or orange so you don't have to write CTB or CTO on it, just put F for full, T for 3/4, H for half and Q for quarter. Simple and unambiguously clear. Use the decimal fractions if you like.

Here's one that is often missed. Note that full CTO takes you from daylight (5600K) to less than tungsten (3200K). It actually converts bluish (6500K cloudy sky) to 3200K. You want 3/4 CTO to get from 5600K to about 3200K.

Because they filter out the unwanted colors of light, full color correction gels greatly reduce the intensity of light. You lose 2/3 stop going from daylight to tungsten and because tungsten sources are weak in blue light you lose 1 2/3 stops going that direction. Losing one stop halves the light.

It's an artistic choice but mixed color temperatures can be visually appealing. Let's say you're doing a bedroom shot and your main lighting is daylight balanced. So white sheets look white. The practicals in your scene, say bedside lamps, will look warm in color. Before you reflexively gel them blue so that their light is also white, have a look. I often like a few warmer colored practicals in a shot. I encounter this a lot when that bedroom scene is illuminated principally with tungsten light. It's common to put the bedside lamps, or whatever shows, on dimmers so they aren't blown out. This reduces their color temperature even more from the warmish 2700K that their lightbulbs are when burning full brightness. Don't gel them, let them be. The warmth will look good. (In my unhumble opinion.)
 
The only party colors, effects gels, I carry are red, green, deep amber and deep blue. I need to pick up some other stuff mainly to use on backgrounds and would benefit from someone's advice. The Tonight Show set uses effects gels nicely.
 
Y'know, whenever I open a short-roll of seamless, I save the plastic bag (after making a bunch of "finally a condom that fits" jokes... yep, I can NEVER run for president...)

Anyway, I sort my gels and use those bags to hold them, rolled up. CTB/CTO in one, diffusion in another, ND and go-to straws, intense colors, etc. I throw all of those into my general-grip & tools case. Since they're clear you can see what's in them, and they keep everything loosely rolled. I've seen those pricey gel cases, and yeah, in a perfect world I'd only take a dozen sheets with me. Those bags are really the bomb, and they're free. Just trim a few inches off.

(Disclaimer: I really can't say if they actually make good condoms though...)
 
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