I was shooting a wedding today with some white drop ceiling, and i noticed when I used the 17MM setting on my 550EX, the lighting looked "weird" but looked better @ the 24mm setting.
What zoom setting do you use when bouncing, with an "open" gary fong..
That depends on the desired result.
Bouncing in intended to create a larger light source, so if the wall or ceiling is close then a wider setting on the flash will help create a larger bounce source.
If the wall is a bit farther away, then a narrower setting will help get more light to the subject. Although it will mean the shadows are a git more harsh.
Think of it this way: the spot where the light hit becomes a virtual umbrella on that spot that will reflect light downward and in the same direction the flash is pointing. So if you want to light up a large area you'd zoom wider. If you want the bounced light to fall on a narrower area, such as the bride and groom cutting the cake with the background fading into the shadows you'd zoom and just create a smaller spot and virtual source on the ceiling. Of course the height and color of the ceiling are also variables which can make bounce flash as predictable and successful as making a three-cushion bank shot in billiards blindfolded.
All things considered you'll have much better creative control of your lighting by using two lights in a key / fill arrangement instead of trying to mimic that type of lighting with a single flash and bounce/diffusion.
