Thanks all!
I will try again this coming weekend.
I took the shot last Saturday afternoon at Marina bay, so the light condition is not an issue.
However I suspect it could be due to my aggressive use of zooming unnecessarily¡K :D
I find it quite difficult to obtain a good focus on a subject although I did using the AF/AE lock.
At least 3 out of 10 pictures I took, the subject(people) are out of focus.... :(
Any help?
Thanks