Say, you are using a AF-D lens with your SB lite. Your F90 and above
will do 3D Matrix Metering for you. When the shutter button is
depressed, the focus is lock-on. At this time, the flash will preflash
to measure the exposure at that distance.
By bouncing, light falls off ceiling distribute more evenly onto the
person's head and down liked sun light. Imagine it as light slowly
decending onto the people in your view finder. Or... A 5X12ft
multi-layer jello dropped onto the crow, the heads of those people within
a few feet will have almost the same amount of color (light). :)
Precious f-stops will be lost during this bouncing light technique.
Also, I would have a flash gun with Guild number of 150+ to do this kind
of job. And I will do it with manual mode.
BTW, if the light is bounced from a "dark/red" wood surface or yellowish
stained glass, light decending on the subject will look funny.
