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Lighting Ratios

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#1 Sawyer Thurston

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Posted 03 February 2018 - 01:54 AM

Hello,

 

I've been trying to learn more about lighting ratios, but it had me wonder a few things. Now I know it's kind of a blanket question and people can do whatever they want, but I'm curious about:

 

1. What are all the ratios that people typically look for? (Key to fill, key to background, etc.)

 

2. On average, is there a rule of thumb for lighting ratios, such as background is typically at least 1 stop under key?

 

Again I know that it is ever changing and it's hard to give it a rule, but I think in a way I'm asking what do you as a cinematographer think as you are setting those ratios?

 

Thanks!


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#2 David Mullen ASC

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Posted 03 February 2018 - 11:45 AM

Lighting ratios usually refer to key-to-fill ratios, not a ratio between the foreground and background.  I don't know of any cinematographers who think in terms of ratios anymore, it might have made more sense when measuring light in foot-candles on set when it was easy to compare two sets of numbers.

 

Also, most shows don't work to a consistent key-to-fill ratio for an entire project -- fill light levels are usually consistent within a scene but not across scenes, that would get a bit boring.  And most people set fill levels in a scene by eye these days since the general approach is to use as little fill as possible, it's more just about having enough ambience to see into the shadows.  But if you need to match the lighting later, or are doing a visual effects set-up, then key, fill, background, etc. levels will be noted down. But few would convert that data, usually measured in f-stops, into a ratio like 3:1, 4:1, etc.

 

It's a bit confusing, I think 4:1 means that the fill is two-stops under the key (one-stop under would be 2:1.) So three-stops under would be 8:1?


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#3 Adrian Sierkowski

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Posted 03 February 2018 - 12:26 PM


 

It's a bit confusing, I think 4:1 means that the fill is two-stops under the key (one-stop under would be 2:1.) So three-stops under would be 8:1?

 

That's how I do it.

 

1:1 Same F Stop Key to Fill

2:1 Key is 1 stop (2x brighter) than Fill

4:1 Key is 2 stops (4x brighter) than fill

8:1 Key is 3 stops (3x brighter) than fill

16:1 Key 4 to Fill

and so on since it's the same effective doubling as you get with your "t stops". e..g T2 is 2x as much light as T1.4, T2.8 is 4x as much light as T1.4 and so on.

 

I'll still do ratios on occasion; normally when I'm working without having the camera "up" and if pre-lighting and also on the scout when I'm thinking about how we'll do a scene. For example knowing I may want to use say a 2K as the Key in the scene, and aiming for a 4:1 ratio I'd then think about a 650 for my "fill" (granted that's a very simple equation).

Other times I'll be looking at the photometrics for a certain head for a certain set up and it's foot-candles at x distance and spread and then work out what other unit i'd use where to "fill."

 

Personally I still find it helpful, but I'm an odd duck out it seems.


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#4 David Mullen ASC

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Posted 03 February 2018 - 04:52 PM

But you're still converting stops into ratios... why not just think in terms of stops needed?  Yes, I can understand it when using photometric data that comes in foot-candles, but then you end up converting that into the likely stop it will give you so I'm not sure that then calculating the ratio is necessary as opposed to figuring out how many stops below the key you want to go for fill.  Saying "16:1" to me is a bit meaningless, I'd have to stop and figure out that it meant the fill being 4-stops under.  But like I said, that's because I don't deal with foot-candles very often.


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#5 Adrian Sierkowski

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Posted 03 February 2018 - 05:05 PM

I dunno; I suppose it's just "quick" in my head but it never really troubled me much; and it just seems a bit easier. I also don't think I'm as much calculating the ratio as I am using the ratio to figure the FC or the stop I'd like to be at. For me, I guess, I start with the ratio I'd like to use and then work from there into either stops or FC. In either case, having the ratio is the start point moreso than the end point. In common vernacular I'd say, in my head, well ok, I like a 16:1 and I'm at a 5.6 so I need 1.4 (in my mind this would read, just a touch) of fill and then I'd work from there. I dunno, for me It works, but also as you mentioned even the nature of metering is on the decline it seems (not that I don't like false colors)


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#6 Sawyer Thurston

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Posted 03 February 2018 - 05:14 PM

Ah yes, I can see both of your viewpoints.

 

I read this great article from wanderingdp: http://wanderingdp.c...ing-ratios-101/

 

That's what had me wonder in the first place since he at some point measures Key to Background. But I would imagine that in particular wouldn't have to be a ratio but just X number of stops over or under. Does anyone have a personal rule of thumb as a minimum standard for the background to key? By that I mean like if someone said "at least 1 stop over or under from the key to add depth or else it can easily look too flat." - just curious, perhaps I phrased that too odd.


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#7 Adrian Sierkowski

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Posted 03 February 2018 - 05:22 PM

I think it really depends on what you want your background doing (and what it's made out of). I like my backgrounds under key; but I never much think how much under, unless i'm trying to throw some "mystery" to whatever the subject of the shot is. And other times it's perfectly fine to have a  hot background (large windows for example) so long as it's not TOOOO hot or a "flat" image if that's what you're going for for whatever reason (comedy often comes to mind).


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#8 David Mullen ASC

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Posted 03 February 2018 - 05:22 PM

I think it all depends on our frame of reference, how we see things in our head.  If I used ratios all the time, then a "16:1" ratio would create a picture in my head from experience, but for me, I'd have a faster picture in my head if you said "the shadows are four-stops under key".   But you are right that if working from photometric data in foot-candles, you'd be figuring out how many foot-candles for fill versus for key, which would essentially give you a ratio if you decided to right it down that way.

 

If I read that the key light was going to give me 100 fc at the distance planned, and I wanted the fill to be 4-stops under...  I'd mentally go "50(-1), 25(-2), 12.5(-3), 6.25(-4)... OK, I need 6.25 fc for the fill".  

 

But of course, if I was used to working in lighting ratios and knew I wanted a 16:1 ratio, then it would be easy to calculate that for a 100 fc key, I'd need 6.25 fc fill just by dividing 100 by 16.  But I'm so used to thinking in terms of stops up or down.


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#9 David Mullen ASC

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Posted 03 February 2018 - 05:29 PM

The thing about that article is that in most of those examples, the background was probably not lit separately from the face except for maybe the shot in "The Master" where the wall is farther back.  And in some of those examples, the walls were white so there can be limits on how dark they are going to go relative to faces anyway.

 

In an old-fashioned movie lit with hard spots, you'd light the walls separately from the actors unless they were very close to the wall, so you could decide more precisely how bright or dark to make that wall compared to the face.  But with today's use of practical lighting plus soft lights you tend to light the space to what feels natural to your eye and balance by eye between the actor and the background when they can be separated.

 

Occasionally you get a wall that is so dark in texture, or pure white or reflective metal, that it needs some special treatment.


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#10 David Mullen ASC

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Posted 03 February 2018 - 05:31 PM

Also "traditional" lighting ratios in foot-candles (or stops as measured by incident meters) don't take into effect reflectance of objects such as would be read with false colors or a waveform.


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#11 Michael Rodin

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Posted 03 February 2018 - 06:56 PM

I'd say there are no "rules of thumb" or exact numbers, because it comes down to how your imaging chain (neg->print or camera->grade->projector) handles contrast. There are some books specifying something like "1:4 key to fill for a moody portrait" but frankly it's just oversimplified BS...

 

You always start with testing your stock or camera for over/underexposure. You set up a scene with gray reference and light/dark textures of different lightens  -  makes sense to test with a flesh tone as well. Grade, print, project, figure out your EI, and you see what kind of tone and color, say, -1, -1.5 or any other exposure gives you.

Then, doing your lighting, you imagine how the projected frame should look and choose the correct tone/color for the different parts of the frame, and from tests (and theory - sensitometery does help...) you know how much lighting contrast you need.

The approach is not that far from still photographers' zone system - but don't confuse yourself with numbered zones - they equal one zone to one stop, and it's incorrect applied to cinema.


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