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Thread: How many foot candles do I need?

  1. #1
    New Orleans, LA
    Join Date
    Oct 2004
    Posts
    563

    How many foot candles do I need?

    There's a photograph I want to take at dusk that will need artificial lighting and I want to use continuous lighting. There is a local rental house that provides lighting for the film industry and the fresnel lights I'd like to rent have specs of X foot candles at 20 ft. How can I determine how many fc's I'll need for a given f-stop? Let's say f45. Would like to keep the shutter speed above a second, higher if possible. The lighting choices are 10K, 5K, 2K, and 1K. Is there some simple math for this problem? My head is spinning with foot candles, lumens, EV values, etc. but I want to make sure I get the math right.

  2. #2

    Join Date
    Feb 2016
    Location
    So Cal
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    53

    Re: How many foot candles do I need?

    One of the few things I remember from 1970s film school, largely because it was beaten into us, is "basic exposure rule":

    ASA/ISO 100, 1/50th @ f2.8 = 100 fc

    f2.8 > f45 is 8 stops, so you'll need some combination of film ISO, shutter speed, and lighting to get there. For example: ISO 400, 1/2 second, f45, 200 fc, if my math is correct.

    After that, the other factor for the fresnels is light-to-subject distance and inverse square law.

  3. #3
    New Orleans, LA
    Join Date
    Oct 2004
    Posts
    563

    Re: How many foot candles do I need?

    Exactly what I needed! Thanks!

    Quote Originally Posted by EarlJam View Post
    One of the few things I remember from 1970s film school, largely because it was beaten into us, is "basic exposure rule":

    ASA/ISO 100, 1/50th @ f2.8 = 100 fc

    f2.8 > f45 is 8 stops, so you'll need some combination of film ISO, shutter speed, and lighting to get there. For example: ISO 400, 1/2 second, f45, 200 fc, if my math is correct.

    After that, the other factor for the fresnels is light-to-subject distance and inverse square law.

  4. #4

    Join Date
    Sep 1998
    Location
    GA
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    12,526

    Re: How many foot candles do I need?

    Quote Originally Posted by Thom Bennett View Post
    Exactly what I needed! Thanks!
    And color temp of the lights, ambient light and whatever you will record on!

  5. #5

    Join Date
    Dec 2009
    Location
    Pacifica, CA
    Posts
    1,626

    Re: How many foot candles do I need?

    You could pick up a Weston Master III which has a foot candle scale and ASA film speeds. (Older Weston’s are off a bit from ASA). You don’t even need the meter to be working, just dial in what you want to set on the camera and look where the needle would have to be.

  6. #6

    Join Date
    Sep 2003
    Location
    La Luz del Oeste, Albuquerque NM
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    511

    Re: How many foot candles do I need?

    Well, if you already have two candles, one in each hand, then I'd say you just need two more for each of your feet.
    Peter Collins

    On the intent of the First Amendment: The press was to serve the governed, not the governors --Opinion, Hugo Black, Judge, Supreme Court, 1971 re the "Pentagon Papers."

  7. #7

    Join Date
    Nov 1999
    Location
    San Clemente, California
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    3,348

    Re: How many foot candles do I need?

    Quote Originally Posted by Peter Collins View Post
    Well, if you already have two candles, one in each hand, then I'd say you just need two more for each of your feet.
    I was going to reply "eight." One between each pair of adjacent toes on each foot. They're foot-candles, after all, not hand-candles.

  8. #8

    Join Date
    Dec 2000
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    Tonopah, Nevada, USA
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    Re: How many foot candles do I need?

    https://www.sekonic.com/united-state...sionchart.aspx

    Our 70 year old Fastax Light Candles meter that I don't have the heart to get rid of at our lab.
    Attached Thumbnails Attached Thumbnails FastaxLightCandles1949.jpg  
    He is no fool who gives what he cannot keep..to gain that which he cannot lose. Jim Elliot, 1949

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