[MF3D.FORUM:1480] Re: NSA MF slide show

["Bill Glickman" <bglick@xxxxxxxx>]

Tom

> 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.

        Totaly agreed.....here is some notes from my flash cheat sheets...

double  distance = 2 stops less light
1/2 distance closer = 2 stops more light
Double ASA = 1.4x more distance
4x ASA = 2x more distance
Half ASA =  30% less distance

        So if you double the distance, you get 2 stops less light, or 25% of
the original amount.  This matches what you state above...  I find it easier
to deal with stops in the field since that is how the meter reads...

        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




>
> 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
>