[newbie]

Thanks a lot for your help, 2006 :)

So you mean "focus in" mainly refer to the act of looking carefully at somthing, while "focus on" has the same meaning, but it often refer to the abstract meaning "concentrate on"?

And sometimes "focus in" can also be used the same as "focus on"? (Your last example "You have to focus in class")

Many thanks
Newbie