[MF3D.FORUM:1494] GN for Multiple Flashes (Was: NSA MF slide show)

["Michael K. Davis" <zilch0@xxxxxxxxxxxx>]

Hi!

At 03:10 PM 2/10/01 -0800, you wrote:
[snip]
>        Now, the one issue I am still trying to work out is if you fire a
>one flash twice, does that equal the same as if you had a stronger 2x guide
>number flash to start with...hmmmm I will have to research that one, any
>suggesions?
>
>Bill

Here's the math when multiple units are each at the same distance from the
subject or when a single unit is fired multiple times from the same
distance (multiple exposure):

   GNtotal=sqrt((GN1*GN1)+(GN2*GN2)+(GNn*GNn))

GNn is for the nth flash unit's guide number, so you can add as many
flashes as you want to this formula.
  
So, two identical flash units (or two firings of one flash unit) will give
you one more stop, four units will give you 2 more stops, it takes 8 units
to get 3 more stops, etc.

Mike