Help playing Prelude in E Minor by Chopin?

Question

How long do the naturals last? Most of the time I can figure it out by they give me a natural on F (and, the piece being in e minor, it is normally sharped) and I am wondering how long I need to keep it flatted.

Answer 1

The natural remains in effect on every subsequent f in the measure, unless a sharp designation appears.  In the next measure, the f automatically reverts to f# as defined in the key signature, unless another natural designation is applied.  

(As a convenience, a composer will typically note the sharp on the f in the next measure, but is not required to.)

Hope that helps clarify it.

Answer 2

Think of those f's as anticipations of the F sharps... in a way, it's almost like the flatted thirds in blues... if you slightly anticipate the f's then really hold on for a bit before the F sharp, you'll find the most power...

It's  a little like catch your breath, hold it, then breathe out.

It's a lovely piece when you get the feeling.