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When to use Footcandle readings


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#1 Eric Soto

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Posted 24 August 2017 - 10:03 PM

 Hey everyone, I am still learning how effectively to use my light meter. The conclusion I've come to, not that it is correct which is why I am asking, is that I use my light meter  to measure the differences in F stops of light sources. When scouting a location to get readings of practical lights I use fc readings, to see what extra lights I will need to bring. I understand the mentality of " it doesn't matter how you use the tool, as long as you get what you want from it" but I would just like to know how you guys with more experience use your light meter, specifically when it comes to metering light in FC. 

 

Thank You.


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#2 Adam Frisch FSF

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Posted 26 August 2017 - 02:31 AM

I don't use them on video at all, but back in the film days it could be useful to get a FC reading because it's something you can easily communicate to a gaffer. "That bulb is 100fc's, the others are 40fc, and I need them all to be the same". That's easily measurable and understandable. It gets slippery when you have to give them an ISO and an F-stop for them to match instead...


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#3 Brian Drysdale

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Posted 26 August 2017 - 04:29 AM

With video I suspect FC readings are probably more useful on larger lighting rigs, with more lights and possibly where sets are spread across a number of rooms, allowing the gaffer to rig the lighting on their own. TV studio lighting people would do the same, leaving the fine adjustments until they have pictures..  .


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#4 David Mullen ASC

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Posted 28 August 2017 - 10:39 AM

Doesn't matter whether you use footcandles or f-stops but with f-stops you have to know the ISO, frame rate / shutter time and you would tell your gaffer all of that for their meter... but these days that's not hard if you tell that person that you want to get an f/2.8 key at 500 ISO at 24 fps with a standard 180 shuttter angle. Same goes for fill. I don't work in footcandles other than when looking up photometric data.
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#5 Eric Soto

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Posted 28 August 2017 - 12:06 PM

Doesn't matter whether you use footcandles or f-stops but with f-stops you have to know the ISO, frame rate / shutter time and you would tell your gaffer all of that for their meter... but these days that's not hard if you tell that person that you want to get an f/2.8 key at 500 ISO at 24 fps with a standard 180 shuttter angle. Same goes for fill. I don't work in footcandles other than when looking up photometric data.

 

 

This might seem like a redundant question. But lets say you are scouting a location and you go to a living room with some practicals in there but they are turned off. And you have a corner of the room that has a window to the outside. To meter the sunlight coming through, in order to know how much lights you need to bring for the shoot, what would you meter with? F stops or FC ? and why would it be more efficient to do so. I really appreciate the feedback from everyone. Thanks. 


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#6 David Mullen ASC

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Posted 28 August 2017 - 02:55 PM

I think I answered that... there's no difference if you supply the ISO, frame rate and shutter speed. If you don't know what that's going to be or don't want to work with approximate values and transpose them later, then work in footcandles. I'm probably the wrong person to ask though because I've never gotten into using footcandles!

I mean, if the light by the window is f/11 and the other part of the room is f/2.8, you can figure out the difference between the two whether in footcandles or stops, i.e. "I need to reduce the window light by three stops and increase the room level by two stops IF I want the same level" (it's rare that you'd light a room to the brightness of direct sun). Or you can work in footcandles. Same difference.
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#7 David Mullen ASC

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Posted 28 August 2017 - 02:58 PM

Footcandles tend to be useful -- for example -- when you want to know if you'll have enough light to light an entire field at night with one 18K HMI up on some hill at a distance. You can look up the photometric data for the light, figure out what stop you are going to be at.

Figuring out lighting ratios is also easier in footcandles.
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#8 Eric Soto

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Posted 29 August 2017 - 07:44 PM

Footcandles tend to be useful -- for example -- when you want to know if you'll have enough light to light an entire field at night with one 18K HMI up on some hill at a distance. You can look up the photometric data for the light, figure out what stop you are going to be at.

Figuring out lighting ratios is also easier in footcandles.

Interesting, I would've assumed that F stops would be easier for lightning ratios. Thank you for your responses.


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#9 David Mullen ASC

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Posted 29 August 2017 - 08:06 PM

The ratio between 100 fc key and 50 fc fill is 100:50 or 2:1.  So is the ratio between f/5.6 key and f/4.0 fill but you can't divide 5.6 by 4.0 and get 2:1...  and it gets even harder when you are dealing with fractions of f-stops and other ratios.  

 

75 fc key : 25 fc fill is 3:1 but since each f-stop is a doubling or halving of light from the next f-stop, it gets less intuitive that f/5.6 key and f/2.8-4.0 split fill is a 3:1 ratio.


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#10 Eric Soto

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Posted 29 August 2017 - 10:02 PM

The ratio between 100 fc key and 50 fc fill is 100:50 or 2:1.  So is the ratio between f/5.6 key and f/4.0 fill but you can't divide 5.6 by 4.0 and get 2:1...  and it gets even harder when you are dealing with fractions of f-stops and other ratios.  

 

75 fc key : 25 fc fill is 3:1 but since each f-stop is a doubling or halving of light from the next f-stop, it gets less intuitive that f/5.6 key and f/2.8-4.0 split fill is a 3:1 ratio.

Yea that makes sense. Thank you for the help


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