shooting a group of ~12-15 people... at night.

Heyya flash gurus!

Yes... another one of these threads

I was asked to shoot a group of 12-15 people outdoors at night, with the cityscape behind them.

I have my sigma 17-70 that I will most likely be using. But I have a 12-24, and a 70-200 at my disposal too if needed.

For lighting, I have 4 8ft light stands with 32" umbrellas and shoe mount flashes to go with them.

My question is, do I use all 4 flashes, or will 2 suffice? Due to the nature of flashes, would shooting them through an umbrella be smart? even at 1/1 power?

One last thing, I would like to have the cityscape properly exposed. The only thing I can think of is metering for the BG, then adjusting the flashes until the people are exposed, however I'm afraid the shutter speeds would be too slow and would induce movement. Would it be wiser to just shoot two exposures? One of the cityscape and one of the people, then merge the two in PP?

thanks!

Won't the flash illuminate the subjects for a split second, and you can "drag" the shutter to illuminate the background scene? Just make sure the subjects are in a very dark spot so they're lit almost exclusively by your strobes.

I say use as many as will light them fairly evenly from side to side and in the middle.

I used 2 lights here:

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For the most part, I would suggest using two images, one exposed for your background, and another exposed for your subjects - then using layers in photoshop to merge them into one "perfect" image.

im no flash expert but 2 flashes should suffice as long as you keep it at a good distance, ti should cover all the people evenly. then meter for the background to set your exposure. if anything up the ISO to 800 so the shutter speed wont be too long and give you a bit more flash power. also you could add a 3rd strobe in the back for some rim light? .. just some ideas

thanks for the replies the rim light idea is cool, maybe i will give it a go.

i'm just afraid the people in the middle wont be illuminated properly if i have my flashes to the left / right sides.