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Explain Key Level


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#1 Josh Bass

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Posted 23 July 2005 - 09:33 PM

Ok. . .so I see/hear this term "key level" bandied about, and I wonder, what exactly does it mean?

"Stupid Bbutt! Key level is simply the stop at which the key light reads!"

That would seem the simplest explanation, but I swear I've seen a post on this forum to the effect of "sometimes, you can have a scene where nothing is at key level." So the above explanation can't be quite right, can it?

So. . .

What exactly determines the key level? The stop the lens is set to (i.e. if your lens is set to f4, then f4 is key level).

Anyway, just curious. thanks.
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#2 David Mullen ASC

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Posted 23 July 2005 - 11:18 PM

The "key" is the dominant light in the scene to which all other lights are subordinate. So sometimes a backlight can be the "key" although someone might say that the key is any light that hits the actors face other than the fill. Someone could even say that in an extreme backlit situation, the fill is the key. These terms are somewhat nebulous once you move away from the classic 3-point lighting set-up.

We sometimes talk of "key exposure" or "exposing at key" as in exposing the key light at normal brightness rather than under or overexposing it. Basically exposing at what the incident meter tells you to for a correct exposure. So saying that "nothing was at key" means that nothing was ever at normal brightness in the scene.

Sometimes we just say "I keyed the actors with..." as in "the main light on the actors was..."

So we use the word "key" in lots of ways, some contradicting others.

All that matters is that your Gaffer understands what you're saying when you ask for something.

I remember once asking Roger Deakins about how much fill he likes to use and he said "I don't really think of lighting in those terms, key and fill, etc." I don't think he uses fill light mechanically, as something you just always add to adjust the contrast. I think sometimes if he wants less contrast, he simply makes the key bigger and softer so it wraps around more.
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#3 Chris Cooke

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Posted 23 July 2005 - 11:31 PM

What exactly determines the key level? The stop the lens is set to (i.e. if your lens is set to f4, then f4 is key level).

<{POST_SNAPBACK}>


You got it for the most part. I've heard "key level" being referred to as the level that the green/blue screen is at. I think what your asking is, "what does key really mean?" "Key" is whatever f-stop you set your lens to. You may have a scene where everything is under key or where most things are over key. Your "key light" is your primary source of illumination but it may be under or over key.
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#4 Josh Bass

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Posted 24 July 2005 - 01:08 AM

So if I read an article that says:

"blah blah blah (this would be techy jargon), I was open to f4, and had a backlight that was two stops over key.",

then this means that "key" refers to f4, and the backlight was at an f8?

That's all I'm trying to get at.
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#5 David Mullen ASC

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Posted 24 July 2005 - 01:54 AM

"I was open to f4, and had a backlight that was two stops over key.",

then this means that "key" refers to f4, and the backlight was at an f8?

<{POST_SNAPBACK}>


Yes, probably. Although it could just mean that the backlight was two stops over the key light but he didn't necessarily expose for the key light.
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#6 Josh Bass

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Posted 24 July 2005 - 09:44 AM

Ok. I may now possibly kinda perhaps get it.
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#7 Chris Cooke

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Posted 24 July 2005 - 11:54 AM

"Key" is whatever f-stop you set your lens to.

<{POST_SNAPBACK}>


I must qualify that statement. Let's say that you've chosen to push your footage one stop; then key would be anything that's one stop under your chosen f-stop. The same but opposite effect is true when pulling.
You should be always make sure that your gaffer and colorist are speaking the same "language" as you.
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Glidecam

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