Flash Exposure Calc in Large Room

Have to shoot a 60th anniversary gathering in a fire hall assembly room, size approxiamately 40 X 60 with eight foot ceilings.

I have three flashes..580EXII, 420 EX, 540EZ and I am contemplating purchasing the RF 602 transmitter and three recievers.

1. Should i put two flashes one at each end of the room with zoom set to the widest coverage adn the third, say the 420ex in the middle of the room, or put one in each of three corners of the room.

2. For exposure..how would i determine the exposure? use an average setting based on flash readings taken around the room? based on longest distance each flash would be shooting? distance to mid point of room from each flash?

Inverse Square falloff of light will be a killer for 'one exposure suits all' !!!

Imagine setting the 580EXII at 'normal lens' coverage (50mm FF/32mm APS-C) where the Guide Number is (if you believe it!) 130. So 9' from the light is f/15, 12' from the light is f/11, 16' from the light is f/8, 22' from the light is f/6. How would you deal with 3EV of difference in exposure?!

Ceiling bounce helps make variability of exposure more manageable, since Inverse Square does not fully apply when the apparent size of the light source (the ceiling) is large, but when you are trying to reach 20-30' with any given light, it still is somewhat unmanageble to simply leave the lights stationary.

Yes..the more I thought about it, I agree with you. Except I see lighting set ups all the time where the photographers set up flashes around the room and then set them all off wirelessly as they shoot around the room... I just couldnt understand how they would figure there exposure unless they are shooting etl or ttl, however, I have assumed they were shooting manual

I believe they use a combination of manual & ettl settings. Your 40D should be able to simultaneously fire a wireless flash with the pc jack (manual) plus a hot shoe mounted flash(ettl). Does the RF602 have a pc connection?

yes I believe so..so you are saying use the flashes spread around to fire wirelessly and at same time use flash on camera etl?

DarenM wrote in post #8666373
Have to shoot a 60th anniversary gathering in a fire hall assembly room, size approxiamately 40 X 60 with eight foot ceilings.

I have three flashes..580EXII, 420 EX, 540EZ and I am contemplating purchasing the RF 602 transmitter and three recievers.

1. Should i put two flashes one at each end of the room with zoom set to the widest coverage adn the third, say the 420ex in the middle of the room, or put one in each of three corners of the room.

2. For exposure..how would i determine the exposure? use an average setting based on flash readings taken around the room? based on longest distance each flash would be shooting? distance to mid point of room from each flash?

You omitted to say just what your lighting objectives are .. will people be seated? .. standing & mingling about? .. will you need to light a podium? .. etc. Also what are the expected ambient light conditions?

How do you intend to trigger the flashes?

If you have 8 foot ceilings and they are white use that to your advantage and bounce .. the light will be boring but safe. If you're also blending in ambient be sure to gel your flashes to match the ambient.

Don't make this harder than what it really is .. get there early and set up a couple of flashes in the far corners and fire a few off & chimp, then adjust from there.

DarenM wrote in post #8672772
yes I believe so..so you are saying use the flashes spread around to fire wirelessly and at same time use flash on camera etl?

Yes, I saw a thread about a similar application before but can't remember from which site. I just don't know how effective the fill lights are as you move around. My guess is it won't be very consistent.