Ellis Vener , Nov 27, 2006; 09:52 a.m.
lots of high end portrait shooters use the Elinchrom Octabank, the light really is different than from other designs that look similar. BAsically the difference is that the Octabank is similar to an umbrella with the light source pointing into the bowl and that bounced light then comes out through the diffuser. You can get a similar effect by using a large softbox or umbrella (by large I mean about 72" in diameter) with a larger diffusion screen in front of it -- but that isn't as movable and you need at least two extra stands and grip heads in addition to the diffusion screen and frame --and it still doesn't quite look like Octabank light. Proximity to subject is a factor too.
I have read accounts by a former Leibovitz assistant where he talks about how Annie will have her assistants shoot tests a few days before a portrait session where for particular shots they would experiment with single, double and sometimes triple layers of diffusion n the Octabank that she uses with her Profoto heads. If they are going to that much trouble my guess is that they would also try different types of diffusion material as well. Ms. Leibovitz's sessions are similar to large budget film shoots in terms of meticulous thinking, planning, organization, preparation, crew and execution --and budget.