I'm assigned to take a group photo of 60 persons, outdoor at The Padang field, with my subjects facing Singapore Recreation Club and the CBD on the background. The shoot is scheduled at 5:30PM and might drag as late as 6:00PM, including time to set up and directing the group in positions.
The sun will set right behind the Supreme Court building. Based on this situation, I'll be likely to get backlight which causes some exposure challenges on my subjects' faces.
Will it be advisable to use 2 off-camera speedlights (Nikon SB-800 or Vivitar 285HV) to fill in? Should it be mounted with or without umbrellas? I'll be using a Nikkor 17-55mm f/2.8, Nikon D300 camera mode set to Manual, aperture @ f/8 or f/11. Shutter speed will be adjusted after the first couple of test shots. Should my 2 speedlights power set to full (1/1)?
I'm seeking some technical advise here and hope experts here can help me. Thanks in advance.