Simple Lighting Question?

[SoulCapture]

So im planning on getting the Alien Bees AB800 prolly within the next week. It will be my first step into using lights in photography. One thing that really bugs me is how to incorporate the new light into metering for the photos. I wanted to just wait and experiment myself but the more i think about it the more i wanna know right now.
So.. Lets say im shooting a portrait, indoors.. BUT i dont have sufficient light. My settings are iso400, f/4, and shutter is 1/40 (made up just for the sake of the question). I notice that the meter reading says the shot is exactly 1 stop underexpose. How would a light come into this equation? How would the light bring it to a balanced exposure and how would u do it? I shoot with a canon 20d, 50mm 1.8. Thank you

[OsmosisStudios]

You adjust the light to suit the look, and then adjust your settings to suit the light.

so, assuming youre using a softbox and want light only on your subject, you'll use the aperture you need to get the flash lighting you want, and then use a shutter speed high enough to kill the ambient. By the same token, you would use a slower shutter speed to get more ambient in.

When you use flash, you immediately have to do some gymnastics with how you shoot.

[SoulCapture]

excuse my ignorance as i try to reiterate. If you use a flash you just disregard metering for the correct exposure. I shoot trying out different settings until i get the shot i am satisfied with? Is there any foundation to build off of usually?

[Rentham]

Originally Posted by SoulCapture

excuse my ignorance as i try to reiterate. If you use a flash you just disregard metering for the correct exposure. I shoot trying out different settings until i get the shot i am satisfied with? Is there any foundation to build off of usually?

The meter in your camera is giving you a reading based on reflected light. It doesn't know anything about the Alien Bee. Your in camera meter isn't totally useless, as you can get a good baseline exposure (usually 1 or 2 stops under) if you are balancing flash with ambient.

There are two ways you can find a proper exposure with flash. One way is to chimp. Take a shot, check your histogram/LCD, and adjust from there. Rinse and repeat until you have the exposure you want. The other way is to buy a flash meter. Flash meters take incident readings, so they measure the light falling on the subject. You can sync these with your Alien Bee through a cord or wireless transmitter. Then, based on the meter readings, you adjust your camera settings to match and get a good exposure.

[bhursey]

Ya the camera meeter you can just measure your ambient exposure and then tweek the flash to that.. Glad to hear some one else is still using a trusty 20d.. Histogram is your friend in strobist shots.