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searching for an economical lighting kit to throw 20 feet of light at F3.5


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#1 Harry Patrick Falls

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Posted 12 April 2010 - 10:09 AM

Hello all. I am very wet behind the ears in many cinematography departments to include lighting. I have a canon 7D. I am shopping for an economical lighting package that can light an outdoor 20 foot area at night without going wider than an F stop of 3.5. All lights will be 20 feet from the subject. I would like the scent to be exposed similar to the video clip below at 0:28. Thanks.





clip 0:28,
http://www.youtube.c...feature=channel
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#2 Alex Malm

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Posted 13 April 2010 - 11:20 PM

You should ask yourself what ISO you want to shoot at, which is partially dependent on your budget since higher ISO will mean less light is needed although you will be sacrificing with regard to gain and color. then consider looking at rental prices. Because lights aren't cheap.

Here's the basic formula: at 100 ISO/ASA you will need 100 footcandles for normal exposure at F 2.8 (this assumes a 180 degree shutter and 24fps).

Here are some common heads with the distance and incident light intensity (footcandles). This information is courtesy of the Set Lighting Technician's Manual, which is a book I would recommend if this information is confusing to you and you'd like to learn more.

Head vs. Footcandles at Distances Specified

Head 12ft. 15ft. 20ft. 25ft 30ft.
575 HMI 200 89 50 32 22
1200 HMI 600 267 150 96 67
650 Tweenie75 33 19 12 8
1000 Baby 150 67 38 24 17
2000 Junior500 222 125 80 56
5000 Senior356 200 128 89 50
10k Tenner 533 300 192 133 75
1k Mickey 150 67 38 24 17
2k Mighty 300 133 75 48 33
4x4 Kino 32 14 8 5 4
2x4 Kino 16 7 4 3 2

Note: HMI listed are Fresnel.

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#3 Alex Malm

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Posted 13 April 2010 - 11:42 PM

I'll give you an example.

You plan to shoot at ISO 800 since it's a night shoot. But how many footcandles do you need for an f4? For the formula to work all you have to do is double or half the amounts and sensitivity one at a time since one stop up or down is doubling or halving the light that enters the camera, respectively.

Let's start at step one:
ASA F.C. Stop
100 100 2.8

200 50 2.8 Here the sensitivity has doubled so you only need half the amount of light to maintain f2.8
400 25 2.8 Again...
800 12.5 2.8 Again...

800 25 4 Here we have stopped down one stop so we need double the amount of footcandles to maintain normal exposure.


Then take a look at the chart I attached to my previous post and see which heads will give you the footcandles you will need; in this case 25f.c.. You should always give yourself a safety margin of some sort since the light might be up high in the air on a stand or it might have both gel and diffusion, which would cut down on the light even more.

let me know if this helps.
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#4 Harry Patrick Falls

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Posted 24 April 2010 - 10:00 AM

I'll give you an example.

You plan to shoot at ISO 800 since it's a night shoot. But how many footcandles do you need for an f4? For the formula to work all you have to do is double or half the amounts and sensitivity one at a time since one stop up or down is doubling or halving the light that enters the camera, respectively.

Let's start at step one:
ASA F.C. Stop
100 100 2.8

200 50 2.8 Here the sensitivity has doubled so you only need half the amount of light to maintain f2.8
400 25 2.8 Again...
800 12.5 2.8 Again...

800 25 4 Here we have stopped down one stop so we need double the amount of footcandles to maintain normal exposure.


Then take a look at the chart I attached to my previous post and see which heads will give you the footcandles you will need; in this case 25f.c.. You should always give yourself a safety margin of some sort since the light might be up high in the air on a stand or it might have both gel and diffusion, which would cut down on the light even more.

let me know if this helps.


Wow!! You have really helped me out. Your explanation was clearly understood.
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#5 Ralph Keyser

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Posted 27 April 2010 - 06:21 PM

Alex,

Great explanation!
You might double check the numbers in your chart for some of your larger instruments. I would have expected a 5K up around 850 fc (at 10'), and a 10K around 1200. Probably just a typo or a cut and paste error.

Lighting manufacturer's publish this information (usually labeled as photometrics or performance). Mole Richardson is particularly good about making that data available. The numbers should be considered a guideline, as individual instruments vary in their real-world output (for a lot of reasons), but they'll get you in the ballpark.
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