How to calculate required flash power?
I'm trying to figure out some stuff for a shot I have planned. I should go out and do some testing, but thought I'd ask here first.
Its going to be a portrait taken in full daylight. Problem is, I want to use a very large aperture (like 3.8 or so).
So lets say I meter the sky and get something like f/22 at 1/125s. If I use a five stop ND filter, I'll get that down to f/4.
I'll be using two strobes on the subject. The way I calculate it, I'll need the main strobe to meter at f/22 to overcome the ND filter.
Is there a straightforward way to work out how much power that translates into? My strongest strobe is 450Ws. Sound like enough?