[COLOR=blue][SIZE=7][FONT=Courier]I was at the BGT yesterday around mid afternoon and took several pictures, some of which had orbs and some didn't. If orbs are dust in the air, why is it that some pics have them and some don't even when they're taken from the exact same spot within seconds of each other?

simple answer. because the dust will move around. it wont necessarily be in the exact same place when you go to take a 2nd picture. or maybe it just blew off of the camera. it depends on the lighting too, sometimes the light will make the dust on or near the lense more visible.