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Is there any reason for me to learn lux/footcandles?


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#1 Micah Fernandez

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Posted 29 November 2007 - 04:40 AM

I've been hearing a lot of stories on set about veteran DPs who are so used to the lighting craft that they know what t-stop a certain lamp will give them as a certain distance without having to check a light meter. Since I'm still a relative newbie, I was wondering I would be able to make up for my inexperience by studying the relation of lamp illumination and aperture opening in order to be more precise with my selection for renting (especially on lower budget shoots) as well as choosing fixtures more precisely on set. Is this practical, or even possible? If it is something I should already know (or should be learning), is there a lux-f/stop chart somewhere I can consult? What real world factors come into play beyond the manufacturer's photometric specs that should be taken into consideration when on set?

Thanks to all who answer, and I hope those questions made sense. ;)
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#2 Adrian Sierkowski

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Posted 29 November 2007 - 05:27 AM

AFAIK kodak, online, has a FC to F stop chart for all their films online (one per film) on their spec sheet.


http://www.kodak.com...p;lc=en#exptung


for example (5 fc for a F1.4 on 52/7218 as seen on the proceeding linked table)
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#3 Frank DiPaola

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Posted 29 November 2007 - 05:47 AM

Photometrics can make for interesting academic practice and charts can be found on the internet or in the SLT's Handbook. I studied them quite a bit when first learning and still consult them every once in a while when dealing with a new unit. It?s a very handy tool and something I recommend anyone who is serious about lighting learn. Still, there is no substitute for experience because you're never going to consult a chart on set.

In regards to renting units you?re probably not doing production any favors by trying to nail the unit on paper. A 1200W HMI (the most powerful light you can run off house power) rents for about $10 more than a 575W. Not much more to double your output is it? I?m not advocating grossly over estimating your needs but in general err in the side of too much rather than too little. If a light is too powerful you can always drop wire in it. If it?s too weak you?ll just wish you rented the bigger light.
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#4 Adrian Sierkowski

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Posted 29 November 2007 - 05:51 AM

in general err in the side of too much rather than too little. If a light is too powerful you can always drop wire in it. If it?s too weak you?ll just wish you rented the bigger light.


I can't even begin to embarrass myself enough and say how many times I had been in that situation. But, often it's because the biggest units most of the shoots I'll work on wind up getting are 1K lowels.


I always find myself looking at the photometric tables for units, KinoFlos site has some purdy looking graphs, but Mr. DiPaola is 100% right; experience and practice are the best ways to learn to the point where you just "know" what to use. If that makes any sense (and even when you don't know for sure, to be able to deduce)
But, then again, this whole filmmaking thing IMHO is a life-long process of learning. (My dad used to say he had forgotten more than he had ever known)
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#5 Joseph Zizzo

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Posted 30 November 2007 - 11:01 PM

i absolutely agree, there is no substitute for experience.

you definitely want to err on the side of too much light. i use pars all he time for this reason, they give out a ton of light. and we are always bouncing or going through diffusion nowadays, so you need a ton of light. for tungsten work, i love maxibrutes and minibrutes (also called "9-light fay"). they each have 9 pars, individually switchable. (forgive me if you know all of this already.) the minibrute is awesome: it gives you as much light as a 10k, but uses the power of a 5k. then there is the parcan, with one 1k par 64 in an amazingly simple and indestructibe housing that controls a lot of the spill for you. great, cheap light.

you also want to take into consideration, and be able to approximate, how much light a given diffusion will eat up. that said, i must admit that i'm still constantly asking the grips to change the grid cloth to light grid!! slow learner, i guess... but it helps to have a plan B, something you're sure of, that you can fall back on, quickly, if what you're going for doesn't work. and do use those photometric tables, especially when planning a setup where you need tons of light for slo-mo or skinny shutter or whatever... they have saved me more than a few times.

as far as lux and footcandles go, i wouldn't bother. its just a system of measurement, and no one uses it anymore. meters all read in f-stop now - i don't even remember what a t-stop is, i don't think. a very smart dp once said to me, never memorize what you can look up. in other words, keep your mind free to riff. for me, its all about what frank and adrian are saying: its a long-term learning procees wherein you develop your talent by trusting your eye, and in the meantime paying attention to the technical stuff, so you can repeat good results.
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#6 John Brawley

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Posted 30 November 2007 - 11:50 PM

as far as lux and footcandles go, i wouldn't bother. its just a system of measurement, and no one uses it anymore.


Im not so sure about that. I use fc's often when I'm metering. Why ? Because it's an absolute value that ISN"T related to any ASA, Filter, frame rate whatever. It's just *that* much light. So no matter what variables change on the camera side, it's always the same FC. You usually can work out what you want your shooting stop to be, and how many FC's are required to hit that, so in your head you know that 100FC's is your base exposure and I find it's easier to *read* where things will sit in terms of exposure by comparing the FC reading to my base level that I'm exposing at eg....50FC is one stop under..etc....

You would also want to use them when you're tying to calculate how to get a given stop in a studio you've never been into when you want to know how many or what size fixtures to get.

So Im in a large studio, and I want to know that I can hit F5.6 from the grid over a certain area. Get my handy photometrics tables out and off I go. Then Ic an calculate how much power I'll need.

They are usually just a starting point though. The tables are often optimistic and you need to allow a reasonable margin of error, usually on the less side.....(it's usually less from the light than what they say you'll get)

jb
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#7 Chris Keth

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Posted 01 December 2007 - 12:26 AM

They're nice for planning. Know, though, that very often tables' value for a fixture will often be higher than the actual fixture you have. Reasons for this range from dirty fresnels to crappy reflectors and God knows what else.
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#8 Jonathan Bowerbank

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Posted 01 December 2007 - 02:12 AM

Since I'm still a relative newbie, I was wondering I would be able to make up for my inexperience by studying the relation of lamp illumination and aperture opening in order to be more precise with my selection for renting (especially on lower budget shoots) as well as choosing fixtures more precisely on set. Is this practical, or even possible?...


I think this exact question was posted just a few months ago. I remember saying this there as well, but really, the more you know about light and the different ways of measuring it, the better. It also helps to know what FC's any given lamp would have at various distances, especially if you're considering various speeds of film stock and want to get an idea for what would be best considering your light kit.
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#9 Joseph Zizzo

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Posted 01 December 2007 - 08:40 AM

Im not so sure about that. I use fc's often when I'm metering. Why ? Because it's an absolute value that ISN"T related to any ASA, Filter, frame rate whatever.


you're the first dp i've ever heard say they use fc when metering! and when i was a gaffer, i worked with some old-school guys... like haskel wexler, e.g., he expressed his light measurement in f-stop, and he used those fractional thirds-of-stops, like 2.5 and 6.3. the first time he said, i'm "reading a 10 here", i didn't know what he was talking about... until his assistant whispered to me, "8 and 2/3"!

i know many times i have to do the conversion from fc to f-stop in the course of calculating photometrics, depending on how the photometrics table is written. but in terms of using them on set, for me its just an extra mathematical step i don't need in the middle of a shoot. i'd rather just put all the filters and everything right into the meter, and call out the f-stop from there. for me, its simpler...

that said, i do know what you mean, john, in this sense: anyone who uses a petax spot meter, which i do, reads in ev, and then calculates how that absolute light reading relates to an f-stop at a given asa rating. actually i do it the other way, i look up what my shooting stop is in ev, then i spot-meter the set to check the shooting stop. in that sense, i agree with you.
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#10 Walter Graff

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Posted 01 December 2007 - 10:04 AM

I've been hearing a lot of stories on set about veteran DPs who are so used to the lighting craft that they know what t-stop a certain lamp will give them as a certain distance without having to check a light meter. Since I'm still a relative newbie, I was wondering I would be able to make up for my inexperience by studying the relation of lamp illumination and aperture opening in order to be more precise with my selection for renting (especially on lower budget shoots) as well as choosing fixtures more precisely on set. Is this practical, or even possible? If it is something I should already know (or should be learning), is there a lux-f/stop chart somewhere I can consult? What real world factors come into play beyond the manufacturer's photometric specs that should be taken into consideration when on set?

Thanks to all who answer, and I hope those questions made sense. ;)


I think the answer is no. I can tell you how many foot candles a fixture produces at a distance by putting my hand in the light and can tell you what f-stop to set a lens at looking at the scene I am shooting not because I know what foot candles and lux light is from experience seeing it. You used the term veteran DPs and I think that is why you see them able to do what they do. They don't study any charts, they simply put themselves in situations over and over and get to know light. As I try to teach in my seminars and on one of my DVDs on lighting, it's about memory. Learning how to light is not about fixtures but learning how to take pictures in your mind of the quality of light light and various situations you find yourself and then repeating what you remember later. As a kid I so remember the light coming in a window making a beam caused by both its intensity and the dust in the air. I can see it vividly today as if it was yesterday. And as you become more accustom to seeing light and how it looks in various situations, you start to know what the relationships and levels translate to. I could use any number of examples of other areas of life where this is true. Driving a car for instance. Drive a car for a week and its all scary. Drive for a decade and it becomes easy. When IK was young I did a lot of work with socket sets (tightening nuts and bolts on cars) and to this day I can look at a nut and tell you what size socket it needs. I could study charts of socket sets but that would not give me what I need to know what size a socket is in the real world. So I would say find what works for you, use a Meter (FC meter is a great start) and learn what 40 fcs is, and what f-stop that represents, so that you can put the meter away eventually and look at a room and say this is 40 fcs of light, and I know with this film stock my lens needs to be at this stop. Just like a golfer you can't be a pro unless you dedicate the time to swinging that club.
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Aerial Filmworks

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