Choosing appropriate light fixtures (2 replies)
Hello Roger, hi everyone,
I've been studying your lightning setups for a while, and I every time I read your posts one question comes to my mind. How you choose light fixtures (i mean output). How do you know that you need exactly 12k tungsten, not 5k, not 2k, or whatever? Maybe there are some formulas to calculate?
Thank you so much for sharing your extensive knowledge for free!
P.S. Sorry for occasionally bad english, I'm still learning it 🙂
There is a simple rule that comes in handy: you need 100 foot-candles to get an f/2.8 at 100 ASA (at 24 fps / 180 degree shutter). From that, you can scale up or down since everything works in halves and doubles. There is photometric data for movie lamps that can give you foot-candle levels at different distances at spot and flood. You can figure though you'll lose half of that output with diffusion techniques, so it is typical to get a lamp that is twice as bright as you think you need -- you can always drop a scrim in it or dim it.
The truth is though that most of us learn from scaling up our experiences over time. When I started out shooting Super-8 movies on 64 ASA reversal stocks, I had an open-faced 650w tungsten movie lamp to work with, plus photoflood bulbs. When I got to film school, I had access to 1K's and 2K's, a few 5K's in the studio. You start to get a feeling for how much light those units give you so at some point, you realize that you need to rent a 6K HMI, let's say, and a generator for a particular location. And after that, maybe you reach the limits of what a 6K gives you and the next time, you rent a 12K HMI, etc.