Calculating Soft Light Throw

Ronnee Swenton · February 28, 2014

I'm familiar with calculating direct light sources using photo metric data/calculators, but have never encountered a sure fire way of figuring out an exposure for a diffused light. To me it seems like there are too many variables to get it perfect but I'm interested in a ball park or at the very least an "ideal" result.

I wouldn't mind a general answer, but I do have a specific setup I'm interested in calculating for if any one is able to help me.

I'm considering creating a flying moon about 20' vertical (bottom of the 5x5x5 cube). 4 2K Juniors pointed at opposite corners, the entire cube covered in bleached muslin.

I'm trying to figure out what my exposure would be directly below at head height, and what the maximum horizontal distance from the cube I could pull a 1.4. I'm slightly nervous I might need more power, which I imagine will be the case.

Mark Kenfield · February 28, 2014

The photometrics would change vastly depending on the fabric being bounced into or shot through, it would change depending on the beam angle at which a particular source hit it at, it would change depending on both the distance of the source from the diffusion as well as the distance of the diffusion from the subject. So I really can't see any real way to calculate precise luminance the setup would provide without testing it specifically.

Adrian Sierkowski · February 28, 2014

Hell it would even change often substantially with how recently it was last put through the wash. If you are going with one of those helium balloons, however, they may already have rough photometrics on it.

Ronnee Swenton · March 1, 2014

Well with that's said, has anybody every flew a flying moon and what was your setup and resulting measurements? Perhaps I can get an idea by scaling down from somebody else's measurements.