The London Photography Meetup Group organised a charity event in aid of comic relief at Portobello Road market. A ridiculous number of photographers turned up, showered people with leaflets and took portraits galore. I had a 2:30 slot booked and set up a couple of lightstands with white shoot-through umbrellas which I gaffer taped to our market stall and the adjoining stall.
The umbrellas created a cross light at about 45 degrees to the sitters. The rear umbrella was about three times further from the subjects than the front umbrella and contributed a nice soft highlight on the subjects right hand side. The ambient was underexposed by about one stop.
Shooting groups with this setup worked reasonably well. You had to take care not to let people fall into each other's shadow which was difficult in the cramped conditions.
It was a fun hour for me, a little chaotic perhaps, but a great way to raise money for charity. You could construct a little photo booth and create studio quality portraits in just about any location.