lights and gels--effects for color manipulation

[jamessilverman@hotmail.com]

I am a little confused how gels work wiith different kinds of lights.

 

for instance: would it matter if I was shooting on tungsten stock w/ HMI's gelled w/ 1/4 CTO...what happens...is it fully color corrected? or just slightly orange....would it be acceptable.

 

basically i just want to know when a gel... like straws, desighner gels like glacier blue, cosmetics, and correction gels and are put in front of HMI's and tungstens and their effect on the film stock you are using. (daylight and tungsten)....does the color temperature of the light have any effect on the gel being shot through. do i have to compensate extra for the color temperature of the light...or

 

am i over analyzing this gel /color compensation issues?

 

somebody please explain these reletively simple concepts....

 

 

cheers.

james silverman

[David Mullen ASC]

Yes, obviously the color temperature of the light has to be taken into account when gelling. Tungsten is 3200K and Daylight is 5500K, at least in terms of the film stocks.

 

An HMI is daylight-balanced so when used with tungsten stock with no 85B correction filter on the camera, then the image will be blue, as if you used a tungsten lamp with Full CTB gel (Full Blue). To correct an HMI to tungsten (5500K to 3200K), you would use Full CTO (Full Orange).

 

If you only use a 1/4 CTO, then you're still bluer than 3200K -- so it would look like you used a tungsten lamp with 3/4 CTB.

 

To make an HMI look warm on tungsten-balanced stock, you'd FIRST have to use a Full CTO just to get to "white" (3200K) and THEN add more orange gel to get a warmer color.

 

If you used daylight-balanced film, then a tungsten lamp would look orange, as if you used an HMI with Full CTO.

 

But this is all assuming you're shooting in an environment with no natural light. When combining artificial and natural light, you also have to take the color temperature of the natural light into account.

 

A tungsten-balanced film stock sees 3200K light as "white." Hence why a 5500K or so light like an HMI renders blue on tungsten-balanced stock. However, instead of gelling the HMI light with Full Orange to convert it to 3200K, you could use an orange 85B camera filter instead over the lens -- but then everything in the frame is colored, not just individual lights. So while an HMI would now appear white, a tungsten light would appear orange.

 

A daylight-balanced stock sees 5500K light as "white."

[jamessilverman@hotmail.com]

soooo. if i were shooting on tungsten stock...used hmi's with a quarter blue...it would make it less blue....correct?

 

 

how does this apply to non-color correcting gels? (please be explicit)

 

i am still a little confused how to grasp/control color, within the range of film stocks.

 

as i like to utilize alot of color into my scenes and have a hard time getting exactley what i want. should i buy a color temp? or should i pay more attention to the LEE FILTER GEL SWATCH..?

 

thanks

james

[David Mullen ASC]

On tungsten stock, an ungelled HMI is Full Blue and one with 1/4 CTO is slightly less blue than that, but still blue.

 

I don't see how a color temp meter is going to help you become LESS confused. You just need to learn what 5500K light looks like on 3200K film (Full Blue) and then you can imagine something slightly less blue than that. Shooting a test would teach you a lot more than a meter.

 

Or just take a DV or digital still camera and set it to 3200K tungsten preset (light bulb symbol) white balance and look at some normal 5500K daylight on a color monitor and you'll see what 5500K looks like on something balanced for 3200K.

 

Just shoot some still camera tests of different gels and learn what the CTO, CTS, and CTB series do.

 

I don't understand the other question -- gels without color (ND or diffusion) don't really change color temp.

 

If you're talking about party colors like pink or sea-green, etc. you have to imagine them combined with the color of the lamp -- for example, if shooting on tungsten-balanced stock with an HMI, it's the same thing as using a tungsten lamp with Full CTB, right? So if you put a pink gel on an HMI, it's like using a tungsten lamp with Full Blue + Pink.

[Mitch Gross]

The best thing to do is simply look at the color. Tengsten light is a warm orange compared to daylight. So if you use tungsten balanced film and an HMI light (they are daylight balanced), the light would be blue. Add a 1/4 CTB gel and it would be a little more blue. Add a 1/4 CTO gel and it would be a little less blue. Other colored gels -- gels that are not strictly "color correction" but are more for an effect -- are simply the colors that you might wish to have from a light. Want a green light? Put on a green gel. Like something a little yellow? Put on a yellow gel. This is something you do by eye and taste, and that's why there are so many different colors in those gel swatch books. You can mix and match them, double them up, do whatever you want to get the look you like. Some gels eat more light than others and this is noted in the swatch books, but you can also simply meter the light on set or simply look at it.

 

I could sit and describe the physics behind throwing a ball, including stats on angular accelleration, forces of gravity, wind pressure and whatnot. Or I could go outside and toss a ball a few times.

[Brendan Watson]

You don't get angular acceleration from throwing a ball. if you put the ball on a string and swung it around then you would have angular acceleration...

[Mitch Gross]

You are correct, although the swing of one's arm has some angular accelleration force to it. I was trying to make a point, but you are correct in my mistatement.

[jamessilverman@hotmail.com]

"Other colored gels -- gels that are not strictly "color correction" but are more for an effect -- are simply the colors that you might wish to have from a light."

 

so mitch, i essentially just put a gel on the light EX: full straw, glacier blue, flame red, pale amber....and that light automatically becomes that color regardless of the lamp?

 

james

[Phil Rhodes]

Hi,

 

> and that light automatically becomes that color regardless of the lamp?

 

No. I'm not quite sure how you could imagine that would be possible. Filters simply attenuate certain wavelengths. They can't put in what isn't there, and they can't amplify anything, so you're always starting off with what's coming out of the lamp and taking away from it - this is nothing more than the law of conservation of energy. Put flame red in front of an HMI and it will still appear bluer than if you put it in front of a tungsten lamp, although in that particular case the difference is muted because tungsten lamps aren't as deficient in red as they are in blue.

 

The only real complexity here is that if you want a real deep indigo blue, like the colours that are often called Congo Blue or similar (Lee 181) then tungsten lamps simply don't radiate much light of that wavelength, so there's precious little left after the filter.

 

Phil

[Mitch Gross]

James, you are complicating this way to much. Putting a blue gel in front of a light makes it bluer. How blue? It depends on the strength of the gel and the color that light started out at. If all your lights are tungsten and ostensibly the same color, then they will all be shifted by whatever gels to these new colors.

 

Gels don't transform anything into a specific color, they simply shift light transmission towards that part of the spectrum. Pick up a swatchbook and hold it up to different colored lights like a table lamp and the window and you'll see. Ans stop thinking so hard or your head may explode. :D

[David Mullen ASC]

James, just think of an HMI as a tungsten lamp with a Full CTB (Full Blue) gel on it.

 

So it's pretty blue on tungsten film. Putting anything less than Full CTO (Full Orange) will not correct it back to "white" so if you put a 1/4 CTO on the HMI, it's STILL a blue light, just not as blue as it was before.

 

If you put a green gel on an HMI and are using tungsten film, it's basically a blue light with green added to it, so now it will be blue-green.

 

Your light has a color -- and any color gel you add it to will modify that color. If the light is white (like a tungsten lamp using tungsten film, or an HMI when using daylight film) then the color of the gel you add will create that color. But if the light has its own color, then when you add a gel you will get the blending of the color of the gel and the color of the light.

 

If the color of the gel and the color of the light are exact opposites, then you will end up with white light -- hence why a Full Orange on an HMI when using tungsten film will cancel out the blueness and make it appear white on tungsten film. But a partial orange gel, like 1/4 or 1/2 CTO, will only remove some of the blueness.

[jamessilverman@hotmail.com]

thanks guys....my head WAS spinning with all these neurotic uncertainities. cheers

[Lucita Jones]

The following website from the Society of Television Lighting Directors gives a BRIGHTLY COLORFULL explanation on light transmission, filters and color mixing:

 

 

http://stld.org.uk/php/index.php?sectionid...=6&contentid=51

 

 

I would like to learn more about colored light and color mixing but from theProduction Designer´s point of view. Specifically, how DPs and Production Deigners work together in establishing the color scheme of the set. Any suggestions of where I can research on this?

 

Thanks,

-Lucita Jones

[Phil Rhodes]

Hi,

 

Well, right here, if you're asking specific questions. On the odd occasion I shoot any drama, the production design is of central interest to me, and I like to get a working relationship with the production designer as early as possible. The best-looking stuff I've ever shot was also the best-designed stuff. Production designers can make the DP's job a lot easier, I think.

 

Personally I like to apply the same sort of thinking that print designers do - pick a main colour and a spot colour (See: Twin Falls Idaho, green and magenta) but that's just me, and I'm not very experienced.

 

Phil

[Michael Nash]

The Director, DP, and Production Designer are kind of the "holy triumvirate" of the film's look. I like to get together with the Director and Production Designer as early as possible in a film's preproduction to discuss the visual design. Broad strokes of style and references are usually discussed first, then broken down into specifics of color, light and dark, and texture (among many other things).

 

It's essential that the Production Designer and DP collaborate on the look; otherwise the work of each could be compromised or even negated by the other. Likewise costume design and hair&MU are involved also.

 

I try to figure out how I'm going to use color as part of the visual language of the film, and come up with a color palette that's applied for specific characters or specific scenes. It can be stripped down and limited to a couple overwhelming and obvious hues, or it can be deliberately polychromatic for a lively effect. Each film is different.

 

The main point is that all the creative forces are in agreement on how color is being used in the context of the film. I think once the DP and designer see the visual and stylistic references the director brings up, the choices start to become obvious. Ultimately, I think the director should act as a funnel or filter for the ideas the different departments present. Even if ideas are submitted independently, the director should be able to see if they're all going in the same direction. That's also what production meetings are for -- each department head gets to see what the other departments are doing, and discover and resolve issues before they become problems.

[Guest oscar]

some interesting tought is given on Camera Guild site, on "I am Sam" review

and there is a book called Motion Picture and Video Lightning which is very much handy, pretty much clear explained on light transmission, color transmission and the Mired shift value scale, so you can predict at some point how much " colored and in which direction of spectrum" your lights are going to be placed. It's worth buying it, author is Blain Brown, good book.

Cheers

Oscar