[MF3D.FORUM:1478] Re: NSA MF slide show

[Tom Hubin <thubin@xxxxxxxxx>]

David said:

> You can also use one flash and pop it off
> > multiple times, but then you have to do all this math to know
> > just how many times to fire. A flash with a GN of 100 flashed
> > twice does NOT give a GN of 200!

Bill said:
 
>        I will have to research this again.....you could be right...what
> formula do you suggest?

Hello Bill and David,

Two flash lamps or one lamp fired twice should produce the same amount
of light on the subject as one flash if the subject is moved away by a
factor of the square root of two. In general, the GN for multiple
flashes should be proportionate to the square root of the number of
flashes. So you would use 4 flashes to double your distance.

I am basing this on the theory that light intensity is inversely
proportionate to the square of the distance from the light source.  

Tom Hubin
thubin@xxxxxxxxx