Re: Hot Shoe Flash + Umbrella for Group Portrait
I read this yesterday and didn't comment because there are so many variables that you didn't mention.. I agree mostly with Tony though.. to make sure you cover 30-40 people adequately you'll need regular studio strobes of at least medium power. But where does "adequately" start and end..
For instance.. If I was going to make a studio quality group portrait I'd use at least four strobes into large (at least 60inch) umbrellas.. and if was a high quality portrait then I'd use additional lights for effect.
However.. when I shoot weddings it's not unusual for me to light a group that large with a single Quantum T4d into a 60inch umbrella at about 10-13 feet high and centre.. Of course this isn't what I'd call a high quality portrait.. but it fits the occasion and 30-40 person group portraits are not the focal point of a wedding album.. The same setup does very well for individual and small groups however.. but gets very thin with fall off for large groups. I've tried this with Canon 580ex flash heads which are equivilant to your SB-800's and there's just not enough power to fill even a medium size umbrella. You could probably put them on stands and go direct and get away with it.. but again it would depend on your "quality" threshold.
So.. you have expected quality.. how tight you pack the group, ambient light levels, required DOF, tripod to allow longer shutter speeds.., and no matter how you stack it I don't see SB-800's into umbrellas doing the job. I see a semi-adequate portrait with SB-800's in direct mode IF the ambient levels are good, you pack them tightly, use a tripod, and pray a lot..
Someone once gave me this piece of advise that I wish I'd followed a lot earlier than I did. "Buy a Quantum T4D." Since, I've also picked up a couple WL Vagabond units to run my strobes with for on-site portraits when I need a higher quality product.
I hope this helps.