shooting people while using a 580II flash

Been asked to take photos of individual students as they receive awards, in a very large room with indoor lighting.
I'll be using the 580II aimed up and bounced off it's extended white card, (camera - 40D, with 17 - 55 2.8) probably in aperture priority.
Would appreciate any advice on what to do or not do with cam / flash settings.

Thanks

You might want to fill us in with more information like how big is the room and will you be moving around. Also might be better asked in the strobe and flash section. What do you expect to gain using aperture priority?

Put the camera on 1/125 (if possible 1/160) and f2.8 and adjust the iso to the amount of light you get from the flash. With the 55 mm this should give you nice portraits. Adjust the aperture for group shots accordingly.

Actually I read last night that Av won't do well because even with spot metering, the cam will consider all ambient light and might over expose the subject. So perhaps program or manual is better.
I can be as close as I want to the subject receivng the award, so the room size I mentioned doesn't matter. I just want a dependable way to insure my system is metering to the subjects face, and not damaged by ambient light.

Thanks for any advice

Oop's. DRMAX, I sent this before reading your reply. Should I use Av or what mode?

trailguy wrote in post #14424950
I can be as close as I want to the subject receivng the award, so the room size I mentioned doesn't matter.

If you have a smaller room you can use the walls/ceiling to bounce your flash. You also might consider to place a divider or something close to the ceremony to bounce your flash.....

If it is not too late, the best way to do what you are asking is with manual camera settings and manual flash. take ETTL out of the equation.
Have a look at this thread because size of the room does matter. bigger room =more distance for your light to travel=more power required: https://photography-on-the.net/forum/showthre​ad.php?t=451770

Presumably, the light on the stage isn't changing during the ceremony. And, presumably, you'll be able to stay in the same spot during the whole ceremony. Therefore, manual exposure and manual flash power.

If the ambient lighting isn't changing, and the distance to subject isn't changing, you don't need any of the automatic modes - they're just going to work against your intention to have the same exposure across the whole event. The automatic modes are great when ambient lighting is changing, and ETTL is a boon when the distance from flash to subject is changing. But those aren't the case here, so you don't need the automatic modes.

- Use 1/125 or 1/160 to freeze the motion of slowly moving people. They're not posing, so anything under 1/125 will risk motion blur. But they're not leaping and dancing about, either, so 1/400 is overkill. So, 1/125 to 1/160 will be the sweet spot.
- Use a relatively wide aperture to try to separate the subjects from the background of the stage. f/2.8 for best separation between subject and background; maybe a stop smaller for more reliable focusing and maybe a little more image quality (I don't know how the 17-40 does with sharpness and CA when it's wide open).
- Set the ISO so that your non-flashed exposure is underexposed by about a stop.
- Set the flash power to add just enough light to properly expose the subjects on the stage.