A few nice flash photo images I found:
Metering For Flash
Image by unleashingmephotography
The Rule of Thumb
"When using flash, to change the exposure you adjust aperture. Adjusting shutter speed will change ambient light exposure."
Changing Shutter Speed
Your camera’s max flash sync speed is probably somewhere around 1/250th of a second (check your manual for yours). This means that to sync up with the flash correctly, you can’t go any faster. Now compare that with the duration of a flash burst, which depending on the power you’ve chosen, could be somewhere in the 1/4000th of a second range.
So just stop and think about this for a second. Unlike ambient light that builds up on the sensor the whole time the shutter is open, flash light is constant no matter what the shutter speed. The only way to grab less light out of that flash burst would be to choose a speed faster than the burst. But you’re constrained by the max sync speed. So you could change the shutter speed all day, speeding it up, but you’ll always grab the same amount of light from that flash.
The bottom line is that the shutter speed will have no affect on the exposure of the area of your image that’s lit by the flash. Consider the image below. The flash power wasn’t changed, and the aperture was kept constant. I only changed the shutter speed. As you can see, the images all have the same exposure. Had I gone slow enough, I would start to pick up ambient light from the room.
Changing Aperture
Just as a refresher, when you change the aperture, you’re changing the size of the hole in the lens that allows light through. A lower aperture number means the hole is bigger, letting more light in.
So now that we know you can change the shutter speed all day long with no effect, the only other setting to play with is the aperture. If you want to change the exposure of a flash lit photo, simply adjust the aperture setting. A lower number makes your image brighter and a higher number makes your image darker. Take a look at this next series of images, all shot at the same shutter speed, but the aperture was changed.
Simple huh? Just remember that when you change aperture, you’re also changing the depth of field. So if your intention was to get a shot with someone’s face in focus and their body further away out of focus, changing the aperture to a higher number will bring their body more into focus. In this case, you’re better off adjusting your ISO setting, adjusting your flash power, or moving your flash further away.
Info found on Sublime-light.com
