$S$ is a graded ring (over nonnegative integers), $f \in S_{+}$ is a homogeneous element of positive degree, $D(f)$ the elements of Proj $S$ not containing $f$. I don't see the bijection between $D(f)$ and Spec $S_{(f)}$. Here $S_{(f)}$ is the zerodegree part of $S_{f}$ obtained from $S$ by inverting f. I see the bijection from $D(f)$ to the homogeneous primes in $S_{f}$, but is there 11 correspondence between primes in $S_{(f)}$ and homogeneous primes in $S_{f}$?

The homeomorphism $D_+(f) \to \text{Spec } S_{(f)}$ is given by $\mathfrak{p} \mapsto \mathfrak{p} S_f \cap S_{(f)}$ with inverse map $\mathfrak{q} \mapsto \oplus_n \{x \in S_n : x^{f} / f^n \in \mathfrak{q}\}$. This can be checked by simple calcuations. 

