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Thom Bennett
3-Sep-2019, 20:42
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.

EarlJam
4-Sep-2019, 07:03
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.

Thom Bennett
4-Sep-2019, 07:08
Exactly what I needed! Thanks!

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.

Bob Salomon
4-Sep-2019, 10:36
Exactly what I needed! Thanks!

And color temp of the lights, ambient light and whatever you will record on!

Bill Burk
4-Sep-2019, 17:04
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.

Peter Collins
4-Sep-2019, 20:13
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.

Sal Santamaura
4-Sep-2019, 21:02
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. :)

Jim Galli
5-Sep-2019, 08:59
https://www.sekonic.com/united-states/support/evluxfootcandleconversionchart.aspx

Our 70 year old Fastax Light Candles meter that I don't have the heart to get rid of at our lab.