150 person problem

J.W.

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Hello all.

Using a Canon 5D with a 28-135 f3.5 lens and a speedlite 420EX. I will be shooting a group of 150 people at night with little ambient light.
My question is what would be the minimum watt seconds needed per head of a 2 monolight set up? Looking at a 160 w/s or 300 w/s options.

Any ideas would be very appreciated as this job was recently dropped on me, so my anxiety level is quite high.

Thanks in advance.
 
This completely depends on your reflector. You can get reflectors that allow the beam to disperse fairly wide OR reflectors that keep a fairly tight beam so it doesn't disperse much.

The w/sec only describes the source of the light... not how quickly it disperses. And of course distance from the subjects is a major factor as well.

Make life easier on yourself... buy an incident light meter that can meter flash exposures. Then you don't have to guess. Just hold the meter where your subjects will be, trigger the flashes, and read the meter. An incident light meter that can meter flash is one of those accessories that I think should be in every photographer's bag.
 
Good advice from Tim.
As mentioned, the reflector you use is what will determine how much the power (watt seconds) turns into forward light. The wider it spreads, the less light you get in any one particular spot, but you want to get spread that will work for you. The distance the lights are from the group is a big factor as well. To get a spread of light that is nice and even, you'd want to pull the lights back, but that will greatly reduce the amount of light on your group. That's why it's best to have a lot of power at your disposal.

I've heard Derrel mention the PCB parabolic umbrella which is supposed to be very efficient at lighting up large areas. Maybe look into that.
 
We know the light disperses at 299,792,458 meters per second, fast enough to not be worthy of consideration.

We do have to consider the Inverse Square Law, which shows that light power drops off as a square function with distance. I think you will need more than 300 Ws.

How the 150 people are grouped will have a lot to do with how they would need to be lighted, and your lights (and camera) will need to be up high and angled down so people in front don't cast shadows on peoples faces behind them..Lighting the people in the back with out blowing out the people in front will be the big challenge.

Something like this -
150peeps.png


 
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...How the 150 people are grouped will have a lot to do with how they would need to be lighted, and your lights (and camera) will need to be up high and angled down so people in front don't cast shadows on peoples faces behind them..Lighting the people in the back with out blowing out the people in front.
With a groupd this large positioning them is absolutely critical, and until you have that planned out, there's no point in worrying about lights, reflectors or anything else. Since you don't have ready access to a large amount of lighting gear, you're going to need to do a dry run. Get everyone there, find out how best to form them, and once that decision has been made, keep them in position while you measure everything. Also, tell them to remember who is next to them, so that on shoot day you can get herd them in with a little less effort. For a group this large I would also recommend at least two assistants.
 
...How the 150 people are grouped will have a lot to do with how they would need to be lighted, and your lights (and camera) will need to be up high and angled down so people in front don't cast shadows on peoples faces behind them..Lighting the people in the back with out blowing out the people in front.
With a groupd this large positioning them is absolutely critical, and until you have that planned out, there's no point in worrying about lights, reflectors or anything else. Since you don't have ready access to a large amount of lighting gear, you're going to need to do a dry run. Get everyone there, find out how best to form them, and once that decision has been made, keep them in position while you measure everything. Also, tell them to remember who is next to them, so that on shoot day you can get herd them in with a little less effort. For a group this large I would also recommend at least two assistants.

Great tip right there, explore all your settings and options BEFORE "showtime". Stress factor will decrease and pic quality may increase. On a side note group shots are fun if you have the right stuff and are prepared.
 

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