Canon 20D and E-TTL II Flash

In modern photography, the camera is not the cleverest piece of equipment. It still remains a light-tight box that allows a lens to be attached to itself and lets the user set aperture and shutter speed. In many ways, modern digital cameras are no better than the old Rolleis.

However, the flash technology is the most fascinating development. It is amazing what the modern flashes (strobes or speedlights) actually do to almost entirely eliminate the user's input.

On the Canon 20D this is how you use the flash:

Set the camera in Evaluative metering mode.
Attach and EX rated flash (this allows E-TTL metering to take over)
Use the various focussing points to focus on the subject (do not focus-and-recompose)
Fire away at will

If you don't like the flash light coming straight into the face of the subject, try bouncing it off the walls. Various effects can be achieved by bouncing it off side walls or ceilings.

Shoot a grey-card from time to time to get your white-balance right during post-processing.

What the flash actually does:
Once you set the focussing point on the subject, the flash pre-fires a small burst of light. Based on the reflected light in the various metering zones, it figures out the total light needed with the actual firing. Now the curtain opens, the flash fires and the curtain closes. This technique makes sure that the subject is properly lit.

The one drawback to this technique is that some people have very fast reaction time and might blink on the prefire. Cest la vie...