>does anybody have an idea of how "powerful" a novatron 240ws unit is with 3 lights?
> I'll be shooting at a wall probably 24 feet away, and the width of the scene will probably be 15 feet.
>This scene will have models in the foreground about 6-10 feet away. So I'm thinking F 11-16 would be great.
I use a bigger rig - a Speedotron Blackline 2400w/s studio flash with three heads. It is actually like three flash generators in one, a 400w/s, a 800w/s, and a 1200w/s, which can all be ganged together, should the need arise. It is too powerful a unit for most around the house shooting, but when doing cast photos at theatres all units get pressed together.
I have actually modified it to put out less light when I use it around the house, so that it acts like a 200-400-800 w/s unit.
In this configuration the 400w/s channel, when split between 2 heads is handy at 6-10' I use a 30"x40" soft box at 45 degrees for the main, a passive white or silver reflector as the fill, and a hard 7 or 11"reflector for the other head to light the background. I find with 100iso rated film, that I get f/11 at distances of 5-6' from this soft box.
So your contemplated 240w/s unit might not give you as much light as you are hoping for if you are splitting it among three heads, particularly if you are using them with umbrellas or bounced off panels, which tends to cost you at least a stop in each case.
Medium format, with this reduced depth of field relative to 35mm tends to demand more light for the equivalent effect.
I would suggest, if possible, rent studio gear, and learn how it works, before buying. Even if this means setting the light on a stand at the rental shop, and popping it with the planned light modifier in place into your flash meter at the correct distance, or against a grey card, and shooting that with your digigizmo to evaluate exposure.