Erm, if the lighting is stable then quick. If there is light variation then it takes a moment or two to adjust before snapping. Faster than my N4 though. Of course it's difficult to say without comparators, perhaps someone can give their opinion compared to a G2 or a S4.
See for yourself: http://youtu.be/o8PgBrXEZeo
See for yourself: http://youtu.be/o8PgBrXEZeo