  We report on a thorough optical investigation over a broad spectral range and
as a function of temperature of the charge dynamics in
Ba(Co$_x$Fe$_{1-x}$)$_2$As$_2$ compounds for Co-doping ranging between 0 and
18%. For the parent compound as well as for $x$=0.025 we observe the opening of
a pseudogap, due to the spin-density-wave phase transition and inducing a
reshuffling of spectral weight from low to high frequencies. For compounds with
0.051$\le x \le$ 0.11 we detect the superconducting gap, while at $x$=0.18 the
material stays metallic at all temperatures. We describe the effective metallic
contribution to the optical conductivity with two Drude terms, representing the
combination of a coherent and incoherent component, and extract the respective
scattering rates. We establish that the $dc$ transport properties in the normal
phase are dominated by the coherent Drude term for 0$\le x \le$0.051 and by the
incoherent one for 0.061$\le x \le$0.18, respectively. Finally through spectral
weight arguments, we give clear-cut evidence for moderate electronic
correlations for 0$\le x \le$0.061, which then crossover to values appropriate
for a regime of weak interacting and nearly-free electron metals for
$x\ge$0.11.
