Garth Wood <garth@xxxxxxxxxxxxxxx> wrote:
> >If you add a second t32, you will get twice the flash power at 64
> >meters, so you'd only need to pick up 1 stop through aperture choice
> >or film speed. Four t32s would get you 64 meters at iso100 and f/1.
>
> I believe you'd get approx. 1.4 times the flash power (in
> terms of illumination) due to inverse square law. Not that
> my addled middle-aged brain remembers all that well...
>
No, at any fixed distance, 2x the power at the source gives
2x the power at that distance.
Po = k * Pf / r^2
where Po is power incident on the object, Pf is total power of
the flash (assumed uniform over some solid angle), and r is
distance between them. k is a constant that's proportional
to the solid angle of the object from the flash's point of
view.
So if Pf' = 2*Pf, Po' = 2*Po.
If you solve for radius instead,
r = sqrt (k*Pf/Po)
then double Pf, r only increases by sqrt(2)
joey
(who is currently physics-starved because it's been more than
a year since his last physics course... damn eecs degrees)
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