Flash and Then No Flash Due to Clouds??

[Fotoman!]

Ok, let's assume that I am in AV mode with my Canon 7D. It is a cloudy day and I am taking some portrait shots of some soccer players for the team web site. I set my aperture at 4.5 because I want to set it 2 stops from 2.8 which is my Canon lens minimum aperture. I am assuming I will get sharpness on their face but still a little blur in the background of the soccer net about 25 yards behind them. I set my ISO at 400 because it is a mostly cloudy day but with the sun peeking through occasionally. Hence, I will get some shadows on certain players and maybe none on others.

Based on these settings I assume the camera will meter on the player's face (where I focus) and then determine the shutter speed to get proper lighting.

However..... I want to ensure that I get a flash each time so that I don't have some kids with flash lighting and some kids without. Doesn't there exist the possibility that there are no shadows on their face when I take the shot... and hence, maybe no flash occurs? I wanted to keep consistency. I guess a flash every time but just the right amount. I get one chance at taking photos of about 80 soccer kids on a day they all wore their uniforms just for the designated picture day. You don't have a second chance to get it right. I don't want any underexposed kids. I am using an external hot show mount flash.

Thanks for providing your insight. Maybe my settings above are all wrong to begin with?

[wulf]

If the lighting conditions are changing, you will need to make adjustments. Don't rely too much on the flash; it introduces another variable and you will find that the effect of the flash drops off rapidly as subjects move further away.

Are you taking posed shots of groups of players?

Wulf

[i speak in math]

Unless you are in High Speed Sync mode on the flash, you won't sync above 1/250th of a second.