I wonder if anybody can explain why what seem like "light bubbles" appear in flash photographs. I have never noticed it before but in one flash photograph taken recently in a large public space they are obvious and many. I have a Panasonic FZ150 and the manual mentions this effect, says its not a fault with the camera and specifies it's caused by reflections from dust in the air. How is it caused though? (Please dont comment on the quality/ composition of the picture, I know it's awful).
On careful examination of previous flash shots of mine and a friends photos, they are present but I have not noticed them before.