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Lighting Gels


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#1 Matthew Buick

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Posted 20 August 2006 - 05:30 PM

Can anyone tell me about lighting Gels ?
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#2 David Mullen ASC

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Posted 20 August 2006 - 06:17 PM

Can anyone tell me about lighting Gels ?


Can you be more specific?
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#3 Zamir Merali

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Posted 20 August 2006 - 07:19 PM

Lighting gels are see-through pieces of plastic that dont melt when they are close to your light. Some change the colour of the light, some are meant to change the colour temp (for example tungsten to daylight), and some are diffusion that make the light less hard.
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#4 Hal Smith

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Posted 20 August 2006 - 07:33 PM

Can anyone tell me about lighting Gels ?

Look at http://www.rosco.com/ . There's all sorts of information, examples, tutorials, etc., etc. there on gel usage in theatrical, motion picture, and television. They've even got a Storaro Collection of cinegels.

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#5 Matthew Buick

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Posted 21 August 2006 - 11:41 AM

Can you be more specific?


What they are, How their used, How much, stuff like that.
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#6 peter kantor

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Posted 21 August 2006 - 01:35 PM

there are two categories;

1) color corrective gels- used to match/ balance light sources in filmmaking
2) theatrical (party) gels- used simply to add color (technically it removes color) for desired "mood"

these colored plastic film sheets are placed in front of lights, windows, etc. to change the color of the light.
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#7 David Mullen ASC

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Posted 21 August 2006 - 07:11 PM

there are two categories;

1) color corrective gels- used to match/ balance light sources in filmmaking
2) theatrical (party) gels- used simply to add color (technically it removes color) for desired "mood"

these colored plastic film sheets are placed in front of lights, windows, etc. to change the color of the light.


And diffusion gels. And ND gels.

The most common gels used on a production are the blues and oranges to either warm up or cool off the color temperature of a lamp. Full CTB (Color Temperature Blue) is a fairly deep blue that will correct a 3200K tungsten lamp to daylight color temp (although you will lose two stops of output in the process.) Conversely, Full CTO (Color Temperature Orange) is a strong orange that will correct a 5500K daylight lamp like an HMI to 3200K balance to match a tungsten lamp, more or less.

Of course, these gels could also be used for an orange or blue effect as well.

And they make 1/8, 1/4, 1/2 and sometimes 3/4 strengths of CTO or CTB for partial correction, subtle warming or cooling of the color. For example, people often use 1/4 CTO on a lamp to warm up for a night interior scene that should look slightly golden and cosy. They may use 1/2 CTO for a late afternoon effect and Full CTO for a orange firelight effect or a sunset effect.

Some people now use CTS (Color Temperature Straw) instead of CTO -- the amount of correction of color temp is the same for the series, it's just that Straw has more Yellow than Red in their shade of Orange.

Beyond those common gels, you will often use diffusion gels that come in different densities -- the heavier the density, the more it spreads and softens the light but also the more light loss there is.

And there are ND gels, like ND camera filters -- they are gray and just cut the amount of light (ND.30 cuts by one-stop, ND.60 cuts by two stops, etc.)

And then there are the Plus Green and Minus Green (magenta) gels to either get rid of the greenishness of some lights like fluorescents or add green to other lights to help match a fluorescent.

And then there are the party gels that come in strong colors like red, green, blue, amber, purple, etc.
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#8 Hal Smith

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Posted 21 August 2006 - 11:56 PM

And then there are the party gels that come in strong colors like red, green, blue, amber, purple, etc.

And my favorite gel for atmosphere - Rosco R99 Chocolate. Don't give me no "Stinkin' Suede" filter partner, I brung my R99 and it's loaded and lit. :D

Sorry David, I couldn't resist.
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#9 Michael Collier

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Posted 22 August 2006 - 12:16 AM

Best advice I can give if you want to learn color gels (and there are so many variations it can be almost daunting to pic between two shades of green) go to B&H photovideo and pic up the rosco swatch book.

I bought one a long while ago and it has given me a vast feild to play with. I test out new filters before any shoot just to see what I like, or if I find any new favorites. There is somewhere around 200-300 filters included in the book, along with diffusion and some test materials of their scrim material and bounce material(the book itself ran me $110) and they are all 10x12 sheets. Not huge, but enough to cover the barn doors of most 500-100w lights.

Test out all the gels (being careful to mark them with a grease pencil before removing them so you don't get any confused.) Then slate your shot and have a white referance so you can judge the color.

The book also included spectrum-analisys on light loss and gives stops of light loss (very helpfull if you have limited light or power resources and need to plan in advance)

For 110 bucks you can get the ultamate collection of filters to experiment with. (I would recomend buying a few color correction sheets or rolls if your serious about shooting, these are often in short supply on set)

oh, and a humble tip on diffusion (I thought it was an obvious point, but several shooters in my market still don't quite get it): There is no such thing as a soft light ray. there is soft light sure, but one photon can only come from one place and head in one direction. This means that softness is truely determined by the size of the emitter relative to the distance the light travels: meaning if you want very soft light from a long distance you'd better have one big reflector/diffuser!

(another way to put it is diffusion material doesnt surpass the law of line of sight for light. I bring this up because I see photogs all the time put some diffusion material on a light whose barndoors makes for a 6"x6" emitting square, then they place those about 15' away and swear up and down that its a 'soft light')
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#10 David Mullen ASC

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Posted 22 August 2006 - 12:20 AM

From our FAQ Work-in-Progress:
http://www.cinematog...?showtopic=8069

29. What is the difference between hard and soft lighting?

There are many misconceptions and misunderstandings about soft vs. hard light.

Vittorio Storaro describes light as either a point source (which he calls “puntiform”) or a broad source (“multiform”). A point source is a very small, sharp light that creates a strong separation between light and shadow with almost no penumbra (the transition from light to dark.) The shadows created by a point source are very crisp and sharp-edged. At the other end of the spectrum, a broad source creates a very gradual transition from light to dark and the shadows created are very soft-edged if sometimes non-existent. And in between hard and soft light, point source and broad source, are infinite variations from barely softened to super-diffused, shadowless light.

A soft light can be translated into "wrap-aroundness". This implies that the source in itself isn't that important -- it's where you place it in relation to the object that you want to light. The more it wraps around the object, the softer it will be perceived.

The key rule here is that the softness of a light is determined by the RELATIVE size of the source to the OBJECT. In other words, from a photographic subject’s point of view, a 4’x4’ soft source up close and a 20’x20’ soft source farther away may appear to be the same relative size in their field of view. Therefore the softness of the shadow those two light sources create and the amount they wrap around the subject will be the same.

ANY source can be a soft source -- even the hardest spotlight ever created -- if the subject is so close to it that the size of the source becomes relatively larger. The same is true for a large source: it can become hard if far enough away to become very small relative to the subject. The prime example of this is the Sun, which is a huge object in space but so far away as to create relatively sharp shadow patterns.

Now to our real experiment: Get the "hardest" source you can find, like a 4K Xenon spotlight and light it up. Put on some sunglasses to protect your eyes and then hold up a golf ball just in front of the lens. Look at the light on the ball -- is it hard or soft?

Now move the same golf ball 30ft further down the beam and have a look at it -- is it hard or soft?

You will notice that the light was extremely soft in the first instance (although incredibly bright probably), but not in the last. This is simply because the SIZE of the source RELATIVE to the OBJECT in the first instance was very big -- i.e. the source was much bigger than the golf ball, therefore creating good "wrap-aroundness". Further down the line, the source hasn't changed size, but RELATIVE to the object it has done so significantly and has now become hard.

This is the Holy Grail right there: it really has got nothing to do with the source itself -- it's the size of the source compared to the object. Therefore a KinoFlo bank of fluorescent tubes, often referred to as a soft source, is ONLY a soft source if it’s lighting something SMALLER than itself. But it can just as well be used as a hard source if placed far away, OR if lighting a bigger object than itself. Therefore every source can be both hard or soft. But in practical terms, a KinoFlo is generally a soft source because it is often used in close proximity to the subject, not placed very far away as a key light.

The most common ways of creating a soft source is to either bounce a light off of a large surface or shine it through a large frame of diffusion material. But sometimes someone will shine a big lamp through a huge frame of silk, figuring that a very soft source will be created, and find the results not as soft as they had hoped for.

Why?

Simple… because if you LOOK at the silk, you will see a hot spot (usually star-shaped) in the middle where the big lamp shines through it. This means that the hot spot is the primary source, not the overall frame of silk, and since this is smaller relative to the object you’re lighting, a harder light results. You need to completely and evenly fill the frame of diffusion in order to take full advantage of its size.

One solution is to use a very heavy material that is an efficient diffuser of light (unfortunately silk is not that material). Stretched muslin, Full Grid Cloth (nylon), or heavy plastic diffusion material works well. But often even this is not enough to cause the lamp to spread out enough to fill the frame evenly. Sometime the solution is to first bounce the light off of a large white surface and THEN let that bounced light pass through the large frames of diffusion. Sometimes people will use multiple frames of diffusion in a row to keep softening the light. Sometimes using a less sharp lamp to begin with helps, like a multi-bank unit like a Dino or MaxiBrute.

Of course, there is no rule that you must maximize the softness of a light or that you can’t allow a hot spot to come through a diffusion frame. Some people will shine a light through a very weak diffuser like a frame of Opal gel, creating a barely softened light. Learn to appreciate all the textures in lighting, from very hard to very soft.

So to summarize, soft light is nothing but an exercise in creating a source that is bigger and more even than the object it’s lighting. Therefore putting a small piece of diffusion gel right on the barndoors of a light that’s several feet away will hardly create a soft lighting effect. In fact, in this case, the soft source created by the diffusion on the barndoors is BARELY larger than the lamp itself behind the diffusion, and thus the light created is barely softened no matter how dense the diffusing material is.
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#11 Michael Collier

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Posted 22 August 2006 - 01:30 AM

penumbra



Nice word. I'll have to remember that one. I swear somewhere inside of Mullen is a history buff/PHD of physics.
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#12 David Mullen ASC

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Posted 22 August 2006 - 01:41 AM

Nice word. I'll have to remember that one. I swear somewhere inside of Mullen is a history buff/PHD of physics.


That FAQ post was a written by Adam Frisch with some additions by me.
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#13 Michael Collier

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Posted 22 August 2006 - 03:13 AM

That FAQ post was a written by Adam Frisch with some additions by me.


I stand by my statement.

Though Adam must be pretty smart too. It seems to me in cinematography that art only plays 50% of the job. the other 50% is the technical knowledge needed to answer hard questions on the spot (and thereby ensure that the 'art' was actual artistic intent, not just happy coincidence that you play off as art) I am in awe of all that yall know. I have been trying to get myself to that sort of encyclopedic knowledge (mostly cause when I am at home I have all kinds of time, but when I am on set I don't have much time for technical considerations)

I'm sure others have thoughts on this.
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#14 Shane Bartlett

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Posted 22 August 2006 - 06:50 AM

I see this all the time (putting diffusion on a light 10 or 15 feet away) and have, predictably, never seen much in the way of results. I have asked, but unfortunately I've always been told that doing so softens the source. My thoughts were that perhaps the diffusion acts as a sort of heat-shield for another gel (such as CTB), that it acts as a very weak scrim, and/or that the white diffusion somewhat shifts color balance. Any truth to these thoughts?
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#15 Tim O'Connor

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Posted 22 August 2006 - 04:23 PM

I see this all the time (putting diffusion on a light 10 or 15 feet away) and have, predictably, never seen much in the way of results. I have asked, but unfortunately I've always been told that doing so softens the source. My thoughts were that perhaps the diffusion acts as a sort of heat-shield for another gel (such as CTB), that it acts as a very weak scrim, and/or that the white diffusion somewhat shifts color balance. Any truth to these thoughts?


I think that you're right about the scrim effect. People do what you described and say, "See, a softer
light" but what they perhaps ought to be saying is "See, less light." To them that looks softer.
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#16 Matthew Buick

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Posted 22 August 2006 - 05:13 PM

Thanks for the help everyone, I suppose I will have to buy lighting if I wan't to be a succesful DP.
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#17 peter kantor

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Posted 22 August 2006 - 06:38 PM

And diffusion gels. And ND gels.

..Beyond those common gels, you will often use diffusion gels that come in different densities -- the heavier the density, the more it spreads and softens the light but also the more light loss there is.

And there are ND gels, like ND camera filters -- they are gray and just cut the amount of light (ND.30 cuts by one-stop, ND.60 cuts by two stops, etc.)

And then there are the Plus Green and Minus Green (magenta) gels to either get rid of the greenishness of some lights like fluorescents or add green to other lights to help match a fluorescent.

And then there are the party gels that come in strong colors like red, green, blue, amber, purple, etc.


Ooops! I did forget to mention the N.D. gels. I didn't mention diffusion because it is not a gel. That would make three categories of gels.
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#18 Luke Prendergast

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Posted 22 August 2006 - 06:39 PM

Why do you say diffusion is not a gel?
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#19 Don Bachmeier

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Posted 22 August 2006 - 08:10 PM

"Director of Videomatography"

I like that.

Right in there with 'Photon Wrangler'

-back to our regularly scheduled broadcast...
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#20 David Mullen ASC

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Posted 22 August 2006 - 11:24 PM

Why do you say diffusion is not a gel?


Maybe technically cloth diffusion is not a "gel" (short for gelatin I believe, which gels aren't really made of anymore) by plastic diffusion is a gel.
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