The SB900 has three different beam illumination patterns: Standard, Even, and Center-weighted illumination. I have read comments that the bulb-to-reflector and bulb-to-lens distances are manipulated independantly to yield different beam patterns. I used a D300 with a Sigma 10-20 lens set to 12mm/F8.0, 5ft from a bare wall. A SB900 on camera was manually zoomed to 12mm, 50mm, 85mm and 200mm (note that flash was limited to 16mm with Even illumination; and also could not zoom past 85mm in Center-weighted illumination). I haven't drawn any conclusions from this initial analysis. I think I need to compare more zoom samples. Please chime in and make suggestions and requests on future analysis.