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Achieveing a 256:1 Ratio


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#1 Jamie McIntyre

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Posted 24 April 2007 - 11:19 PM

Today in class we were trying to achieve a 256:1 key fill ratio with diffusion, scrims, flags and 2 1k's. The guy we used had a pale skin tone.

First of all, is that even possible with these lights?

We were shooting on Kodak 7218. 500T.

If these lights are not suitable to achieve this what lights are best to use?

Any help is appreciated! :)
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#2 David Mullen ASC

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Posted 25 April 2007 - 12:04 AM

Wouldn't that just mean using no fill light? What look are you trying to achieve?
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#3 Jamie McIntyre

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Posted 25 April 2007 - 01:03 AM

Wouldn't that just mean using no fill light? What look are you trying to achieve?


We were running camera tests. Testing the film stock etc.

Sorry if it sounded stupid. I don't quite know how to explain it.

Our teacher said 'Id be impressed if you can get a 256:1'. We didn't use any fill light, but it was still only a 64:1. So wouldn't we have needed increase the key light? We tried but couldn't get it above a 64:1.

Does that make sense? Haha Sorry, I'm finding it hard to explain this, I'm still learning.
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#4 Jonathan Bowerbank

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Posted 25 April 2007 - 01:37 AM

Not only do you need NO fill, but you need NEGATIVE FILL.

Your extremely bright key was probably bouncing around and causing some bounced light to not allow you to go past 64:1.

Try putting up some flags or laying & hanging up some duvetyne (commando cloth) on the actor's "fill side"
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#5 Jamie McIntyre

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Posted 25 April 2007 - 01:45 AM

Not only do you need NO fill, but you need NEGATIVE FILL.

Your extremely bright key was probably bouncing around and causing some bounced light to not allow you to go past 64:1.

Try putting up some flags or laying & hanging up some duvetyne (commando cloth) on the actor's "fill side"


We did exactly that. We had black jackets over C stands, over pale arms, on the floor, on anything that was reflecting! We put duvatine in some of the ceiling panels that were reflecting the key light also. We were paying special attention in flagging the key light so it wouldn't spill.

Is it even possible to achieve a 'Negative' fill light haha?

I'm just baffled how anyone could achieve a 256:1. Our teacher said you can go up to 512 and beyond, but isn't that like an 8 stop difference!? :-O
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#6 Jonathan Bowerbank

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Posted 25 April 2007 - 01:47 AM

You could try with a more focused light. Like a xenon or source 4.

Worth a go.
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#7 Jamie McIntyre

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Posted 25 April 2007 - 02:13 AM

You could try with a more focused light. Like a xenon or source 4.

Worth a go.


Ok great! Thanks for your help Jonathan! :)
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#8 Kar Wai Ng

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Posted 25 April 2007 - 02:26 AM

Just throwing this out there...how are you metering? Make sure you're using the flat-face diffuser on your incident meter, or if using the dome then shield out the key with your hand. If you're letting light hit the dome when metering the fill side you might be inclined to think you have a lower ratio than you actually have...
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#9 Jamie McIntyre

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Posted 25 April 2007 - 03:06 AM

Just throwing this out there...how are you metering? Make sure you're using the flat-face diffuser on your incident meter, or if using the dome then shield out the key with your hand. If you're letting light hit the dome when metering the fill side you might be inclined to think you have a lower ratio than you actually have...


Thanks for your comment. Much appreciated.

I'm not sure what you mean by flat face diffuser? Is that when there isn't a dome, it's just a 'white sheet' kind of? If so we were not using that we were using the dome. We were shielding it as much as we could, there were no leaks through the hand or through any reflective surfaces.

:blink:

What's the largest ratio anyone has achieved?
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#10 David Mullen ASC

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Posted 25 April 2007 - 03:11 AM

What's the point?
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#11 Michael Collier

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Posted 25 April 2007 - 03:31 AM

I am very confused by your assignment. Mostly by why someone would ask you for a 256:1 ratio? It seems way outside of films capability (or any capture format for that reason) and at that sort of a ratio it would certainly be a simple black on white sillouette, if the physics of the lens could handle it at all. I would think flaring and spill light would reduce it to a grey frame.

The main reason for my confusion is the actual number itself. 256. Its a strange number, simply because its 2 to the 8th power. Thats what gets me. 256:1 (if the professor has a bad understanding of light ratios) could easily be attempting to say 8:1. an 8 stop contrast range would mean your using 256 times as much light between your key and fill. If you had a fill of 1 foot candel, then 8 stops above would be 256 footcandles key. By contrast a 256:1 ratio would mean if your fill was 1 footcandle, then your key would be 1,579,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,00
0,000,000,000,000 footcandles (1.1579e+77. forgive me if my decimal representation is wrong, thats a lot of zeros to count)

Thats where I stop. Does your teacher confuse the idea of light ratios? Did you understand him wrong? Am I just stuck on the coincidence of the number 256 being a perfect power of 2 (aranofskis pi all over again. 2.31498.....drill to head)? I don't know.
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#12 Jonathan Bowerbank

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Posted 25 April 2007 - 11:35 AM

...I would think flaring and spill light would reduce it to a grey frame.

The main reason for my confusion is the actual number itself. 256. Its a strange number, simply because its 2 to the 8th power. Thats what gets me. 256:1 (if the professor has a bad understanding of light ratios) could easily be attempting to say 8:1...


Key to fill ratios, when working with f-stops works that way. 8:1 would be a 3 stop difference whereas 256:1 would be 8 stops. It's not a coincidence that 256 is a perfect power of 2, that's how it works. (2:1 = 1f dif., 4:1 = 2f dif., 8:1 = 3f dif., 16:1 = 4f dif, 32:1 = 5f dif, and so on and so on and so on...)

As for worrying about flaring...don't think that would be an issue. It's "key to fill" that he's worrying about, so he shouldn't have any lights pointing towards the camera if he only has one light he's using.
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#13 David Mullen ASC

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Posted 25 April 2007 - 11:38 AM

I'm not sure what the point is since shadows go black on film around the 4-stop under range, so why would you ever need to get the shadows 8-stops under?
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#14 Jonathan Bowerbank

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Posted 25 April 2007 - 11:52 AM

I'm not sure what the point is since shadows go black on film around the 4-stop under range, so why would you ever need to get the shadows 8-stops under?


Yeah, I don't know the point either...maybe just to impress an incredulous professor?
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#15 Chris Keth

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Posted 25 April 2007 - 11:55 AM

I'm not sure what the point is since shadows go black on film around the 4-stop under range, so why would you ever need to get the shadows 8-stops under?


It's for a metal video. Blacker than black is so goth. ;)

Seriously, though. It is a pretty pointless exercise. Maybe they're preparing to use 7229. You have to have seriously dark shadows for them to go black on that stock. Not 8 stops under key but pretty dark.
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#16 Jamie McIntyre

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Posted 25 April 2007 - 01:38 PM

I'm not sure what the point is since shadows go black on film around the 4-stop under range, so why would you ever need to get the shadows 8-stops under?


No no, we were just seeing if we could do it. The teacher knew the range of the film was only 4 stops. He just said 'as a bit of fun' if we could achieve a 256:1. It was a cinematography class.

It seems as if i've confused people. Nevermind.

Sorry guys.

Edited by Jamie McIntyre, 25 April 2007 - 01:38 PM.

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#17 John Sprung

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Posted 25 April 2007 - 01:49 PM

Yes, it's pointless except as an exercise to think about controlling bounce light. One thing that helps a lot is distance. Set your light up in one corner of a stage, spotted down and flagged off so it doesn't hit anything but the actor for 100 ft. or more, then hang some black where it does hit the wall. You'll probably be able to make or beat your 8 stop ratio that way. Better yet, go out in the desert on a moonless night. Aim your light up into a clear sky, have your actor on a ladder looking down into the light. With nothing but starlight and atmospheric backscatter for fill, your ratio's probably too big to measure -- like a couple dozen stops or more.

(Why is it that when something's pointless, I have so many ideas on how to do it? ;-) )


-- J.S.
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#18 Jamie McIntyre

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Posted 25 April 2007 - 02:05 PM

Yes, it's pointless except as an exercise to think about controlling bounce light. One thing that helps a lot is distance. Set your light up in one corner of a stage, spotted down and flagged off so it doesn't hit anything but the actor for 100 ft. or more, then hang some black where it does hit the wall. You'll probably be able to make or beat your 8 stop ratio that way. Better yet, go out in the desert on a moonless night. Aim your light up into a clear sky, have your actor on a ladder looking down into the light. With nothing but starlight and atmospheric backscatter for fill, your ratio's probably too big to measure -- like a couple dozen stops or more.

(Why is it that when something's pointless, I have so many ideas on how to do it? ;-) )
-- J.S.


OK cool! Thanks!

I was only asking a question because i didnt understand how it would be achieved, I said that in my original post.

Thanks anyway guys! :)
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#19 Matt Sandstrom

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Posted 26 April 2007 - 06:28 AM

sound like a fun exercise, who cares that it's pointless? ;-) duvetyne does reflect some, so using larger sheets further away could be the solution. i'd also worry about haze. you'd need a dust free and dry room to not get that strong light scatter quite a bit in the air. can you see the beam? if you can that's another light source to take into account. maybe flag it down so it physically can't wrap around the subject?

/matt
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