Assuming that the church is like most churches i.e. rather dark inside, the flash will be your main (only) illumination.
Use your flashmeter to read the light reaching your subject from the flashgun (this could be averaged from the middle and edge of the group, as suggested) - this is the aperture to set on the lens.
Take an ambient light reading from the same spot - this is for your shutter speed, using the aperture previously established. How much slower the shutter speed is compared to your lowest comfortable setting will, in general, be how underexposed the surroundings outside of the flash pool of light will be. Unless you light the background seperately with additional lights or balance the ambient with the flash, the background/surrounds will always be darker than the main subject.
Tricky area but hope all goes well.
OK, I think I get it.
So for example, lets say my crowd of 50 people starts 10 feet away from me, and ends at 15 feet, for arguments sake. What I think you're saying is I can do one of two things:
1) Put flash into Auto mode, set it to f8 (f8 covers the range 10-15 feet according to the dial). It doesn't then matter what settings I have on my camera lens (unless it was really really bright) - I can set it as f5.6 or f8 or f11. The flash will then throw as much light as is needed. Or
2) Set it Manual mode for full flash power and then set the camera lens according to the ranges on the flash dial. Using the example above, again, f8 if the crow is 10-15 feet away.
Is that right?
Thanks Mark. It sounds almost too easy! Fingers crossed then.
Metz 45 CL-4
GN: 45 meters. @ISO 100 @35mm
@f/8, Distance = 45/8 = 5.62 meters = 18.454 feet.
If you use it has bounce flash, you can calculate the distance roughly and see whether you get the coverage.
It isn't to tough.
Bounce is the easiest and most forgiving. For a group it is the best choice.
One of the big things that makes flash seem tough to do right is the size of the flash, bounce is more forgiving and looks more normal because you are turning the ceiling/walls/whatever into the light source for your subjects rather than just the lens of your strobe.
+1 on the bouncing, but the calculator on the flash won't do you much good, as you will lose at least a couple of stops, I would think.
If you can meter the flash with your Sekonic that would be best, or else tilt the flash head and try auto mode on the flash. If you can keep the people together long enough, I'd use every method presented in here.
No matter what, your flash is going o have a hard time lighting that room on it's own, and if the interior is dark wood you probably need to forget about bouncing and use the flash direct.
Hate to say it, but, you may also want to consider multiple shots the could possibly be stitched together using that "numbers" method.
Because, depending on what the group and the room are like, you'll be hard pressed to get good light everywhere, especially since the Metz's rectangular head doesn't match your Hasselblad's format very well, though with the 80 that problem will be minimized.
As I said earlier, bounce the flash into a sheet of white or silver card or a reflector, someone could hold this behind the camera position tilted at 45 degrees towards the group. Straight flash will not work well with large groups, it will lead to a large fall off at the extremes (inverse square law) and hot spots in the middle.
Bounce it off the ceiling. Even if it is dark wood and soaks up some light you will be much better off than with direct flash.
Go ahead and plan on pushing at least a stop as well to maximise the strobe. I would stage the group evenly across the room shoot one half for.six frames then the other half allowing for some overlap. Print the best pic of each half then mount them together on one board like a Hockney. If you have the baby's family in the middle and they are in both frames so much the better. They will love it.
So just Max out the flash bounce it and take a meter reading. You'll be good to go.
Also at f5.6 or f8 use a shutter speed around 1/30 and you'll pick up some glow from any lights in the room.